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Small Travel Trailer Mini Air Conditioner Mount for Rear Window (Temporary)

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Small Travel Trailer Mini Air Conditioner Mount for Rear Window (Temporary)
***Remove AC When Travelling – this is a temporary setup just for use when parked!***

When we purchased our 2020 Scamp 13’, we knew we wanted to store it in our garage for many reasons (see “Why and How We Fit Our Scamp in the Garage”).  However, when we placed our order from the Scamp factory, we didn’t order the AC (but did order the reinforced roof for AC just in case situations changed, see “Ordering Our 2020 Scamp”).  This is because, even after raising our garage height from 7 to 8 feet, our new Scamp would have been too tall to clear the garage opening with the factory rooftop air conditioner.  So, we figured we would just plan trips to take hot weather into account.  And, this strategy has worked really well over the past couple of years (there have only been a few times when AC would have really come in handy — see “No AC, No Problem“).  Ultimately though, we have found that when heading to mountain lakes in the summer months, we need to make stops a bit out of our way or drive non-stop to cross the hot parts of California (e.g. Central Valley or Mojave Desert) to beat the heat.  These heat avoidance workarounds have meant taking less efficient longer routes or very long rides straight to our destination.

When looking for solutions (including more streamlined rooftop AC models), we came to realize that we only needed AC mostly in the summer months (and, even then, only on specific trips).  Rooftop ACs are most convenient — however, they are also relatively expensive (including requiring installation expense, unless you can do that yourself), moderately heavy (sometimes creating roof sag on fiberglass trailers), and can be costly to replace when necessary.  Additionally, even the low profile units we found looked to have questionable clearance to fit in our garage.  Taking into account all these factors, we decided that a temporary removable window AC unit would be perfect for our requirements (e.g. inexpensive, easy to install on a temporary basis, lightweight, and also cheap to replace when necessary).  We also wouldn’t have to carry around the heavier weight of a permanently mounted rooftop AC on every trip (including winter trips).  The goal of this project is to create a stable platform to temporarily and quickly mount the window AC unit when at the campsite (removed for driving) which won’t damage the trailer (e.g. window or fiberglass window frame) and provide insulation against insects and weather.

After considerable research and reviews of different window AC units and also various methods people have used to secure a window AC inside their fiberglass travel trailer’s window, I decided to buy a small Frigidaire (FFRE053WAE) 5,000 BTU unit for room sizes up to 150 square feet (more than sufficient to cool the Scamp 13’s less than 80 square feet of interior living space).  It’s inexpensive (currently around $210 on Amazon), small (16” wide, 12 1/16” high, and 13 3/16” deep), lightweight (43lbs on my scale), rated at only 50db noise level, energy efficient and very well reviewed.  Additionally, others have reported using this unit successfully to cool their small fiberglass travel trailers.  It’s among the smallest and lightest window AC units available and ranks as one of the top brands on Consumer Reports.

Every small fiberglass travel trailer is different and weight tolerances vary.  Anyone attempting to undertake this project should understand there are no guarantees when installing a window AC unit in their fiberglass travel trailer’s window.  Damage is a possibility if the trailer’s fiberglass cannot handle the weight of the window AC (this may be especially relevant for older trailers).  However, many people have used window ACs in their small fiberglass travel trailers for years without incident.  Additionally, even some fiberglass travel manufactures have mounted ACs in windows throughout the years.  Taking all this into consideration and wanting to be extra cautious, I decided on using a wood platform and foot brace under the AC (even though it’s fairly light) which helps distribute some of the AC’s weight onto the Scamp’s bumper (which is welded to the trailer’s frame).  This is designed to reduce strain on the fiberglass window frame.  To protect the window, black pipe foam (like a pool noodle) is used around all edges of the window frame.

I spent around $210 for the window AC unit and $100 for materials for a project total of roughly $310 (I didn’t include the $130 I spent for tools in this total because I will use these tools for years on other projects as well).  So, for just a few hundred dollars (perhaps the cost of a hotel room for one or two nights), this system should provide a small travel trailer years of air conditioning relief on hot days.

The tasks to complete this project can be performed in three stages as outlined below.  The listed measurements apply to our 2020 Scamp 13’ trailer but can easily be modified for other trailers and ACs with different sizes.

Stage 1:  Planning
Measure the rear window opening to determine if there is enough width and height to mount the desired AC model (comparing to the desired AC’s dimensions).  If necessary, it may be possible to cut out a portion or remove the rubber window stop entirely to get the window to open more completely.

Stage 2:  Shopping
I decided to purchase a lot of the items for this project online.  However, I purchased the plywood (as well as PVC) at Home Depot so their staff could do most of the cutting for me at no charge (they only do straight cuts though).  Here’s the item list I compiled to complete the project:

a.  Purchase window AC unit (Frigidaire Window AC Model #FFRE053WAE)
b.  Purchase plywood (and, if you want, have it cut at a big box store like Home Depot or Lowes)

    1. One 4’ x 4’ x ½” thick (or 15/32” thick) panel
    2. One 2’ X 2’ x ¾” thick panel

c.  Purchase Tools (if needed)

    1. Belt Sander (to round corners), extra sand paper for belt sander
    2. Jig Saw (to cut plywood), extra blades for jig saw
    3. Drill
    4. Electric Screwdriver
    5. 5/16” Drill bit (for hex bolts holding Sandwich Plates together)
    6. 3/32” Drill bit (pilot holes)
    7. 2.5” Spring Clamps (6)

d.  Purchase Hardware

    1. #6 x 1” Phillips Flat Head Zinc Plated Wood Screws (100 pack)
    2. #6 x 3/8” flat head zinc plated Phillips wood screws (25 pack)
    3. Zinc Plated Hex Bolts x 5 (3 top, 2 bottom) ¼” -20 4” long
    4. Plated Wing Nut (4 pack) ¼” -20 x 2 packs (need 5)
    5. PVC Pipe 1”x 10’ White PVC
    6. PVC T Connectors for 1” diameter PVC x 2
    7. PVC End Caps for 1” diameter PVC x 3
    8. Black Pipe Foam 1” x 6’
    9. Wood glue Gorilla
    10. White (Glossy) Spray Paint (paint/primer) x 2 cans
    11. 2-Hole Pipe Hanger Straps 1” (4 pack) PVC brackets
    12. Velcro Strap (1)

Stage 3:  Construction (also refer to video)
Safety:  Always wear safety glasses for eye protection when working with power tools.

Interior Window Frame:
The purpose of the Interior Window Frame is to provide a stable space for the AC to be positioned into as well as protect the travel trailer’s window frame (so the AC doesn’t sit directly on the fiberglass).  The AC sits inside the Interior Window Frame (on a wooden platform) which sits against protective foam which surrounds the window (although there wasn’t enough window opening space on my Scamp 13’, even after removing a section of window stop, so no pipe foam was put on the outer side of the window  – though I added insulation on the AC interior to fill the gaps).  So whatever AC is used, it’s vital that the frame be large enough for the AC to fit inside it (but not too large, so the frame still fits snugly inside the rear window and doesn’t leave a big air gap).

It may be difficult to cut long lengths of wood with a jigsaw perfectly, so I recommend that, unless one has a circular saw, have a store like Home Depot make all the straight wood cuts.  The jig saw is absolutely fantastic and easy though for making the curved corner cuts (as well as the belt sander to smooth out the curves).  In this project, just the corners need to be rounded and the middle section of each sandwich plate needs to be cut out)

a.  Top & Bottom:  Cut two 16.5” long x 2.5” wide x .75” thick pieces of plywood
Carefully drill 5/16” holes (evenly spaced top and bottom) through the center of the .75” thick pieces, drilling through the entire 2.5” width so 4” hex bolts can pass through.  Three top holes 2” from each edge and one in the middle (all centered on frame), two holes in bottom corners 2” from each edge (a drill press makes this easier, I borrowed one from a neighbor)
b.  Sides: Cut two 14.25” long x 2.5” wide x ½” thick  (I had Home Depot cut these)
c.  Add wood glue onto ends of Top & Bottom pieces
d.  Position sides over the ends of these pieces
e.  Use #6 x 1” Phillips Zinc Plated Wood Screws (8) to join top, bottom and sides (use 3/32” bit for pilot holes if desired, otherwise just apply some pressure to start the screw into the side)
f.  Cut Black Pipe Foam and pad all sides of the rear window opening
g.  Once the square Interior Window Frame is Glued/Screwed together, position it in the rear window of trailer to make sure it fits. Remove a section of rubber window stop (see video) and/or use belt sander to round outside corners if it is too tight to fit.  The side window foam may also be removed if it is still too tight to fit the Interior Window Frame inside the trailer’s window (insulating foam can be pushed into gaps later when setting up at the campsite if necessary).
h.  Slide the square Interior Window Frame over the back of the AC to make sure it can slide almost all the way to the front of the AC (it should stop about an inch from the front due to protruding flanges on the AC).
i.  Fit the square Window Frame into the rear window (pipe foam will hold it in place)

Window Frame Sandwich Plates (Inner / Outer)
The purpose of the Window Frame Sandwich Plates is to hold the Interior Window Frame securely in place and provide insulation from insects and weather.

  1. Cut two 21” wide x 18” high x ½” thick pieces (I had Home Depot cut these)
  2. Trace round back outside window curves onto paper, apply by pencil to above pieces.
  3. Use the jigsaw and belt sander to round each outer window piece (watch video), also slightly round the window corners in the center of the trailer window to eliminate sharp points which can cause damage in transit
  4. Have a partner hold Outer Sandwich Plate in place over outside of rear window, completely covering the opening and level, and, on the inside of the trailer, use a pencil and mark the interior outline of the window frame on the inside of the Outer Sandwich Plate
  5. Use jigsaw to cut marked middle hole in Outer Sandwich plate (first start by drilling 5/16” holes in each corner so that the jigsaw blade may be inserted)
  6. Use outer Sandwich plate as template to mark middle hole position in Inner Sandwich Plate and use jigsaw to cut marked middle hole in Inner Sandwich Plate.
  7. Now, both Sandwich plates should have middle holes to allow the back of the AC to pass through
  8. Line up the Interior Window Frame with the Inner Sandwich Plate on a table and push a pencil through the 5/16” holes to mark the five holes in the top and bottom of the Interior Window Frame (3 marks on top and 2 marks on bottom). Then use these marks to drill 5/16” holes in both Sandwich Plates (using one as a template for the other).  These are for the hex bolts to pass through.
  9. Glue/screw (#6 x 1” Phillips Flat Head Wood Screws x 12 – three on each side) to attach the Interior Window Frame to the inside of the Inner Sandwich Plate (make sure no parts of the plate rise above the Interior Window Frame opening so the AC will continue to pass through unobstructed)
  10. The five Zinc Plated Hex Bolts (six ¼”-20, 4” long) will go all the way through the two Sandwich Plates, and wing nuts on the outside of the Outer Sandwich Plate will hold both Sandwich Plates tightly against the Interior Window Frame (and the plates against the foam on the inside and outside of the trailer). This will hold the window frame assembly securely in position and prevent the AC from falling out of the trailer.
  11. Now assemble the complete window frame by bolting together the Inner (with the Interior Window Frame attached) and Outer Sandwich frames, securing the five hex bolts with ¼” -20 Plated Wing Nuts on the outside. Note:  I had to remove part of the rubber rear window stopper because the rear window didn’t open enough to allow the Interior Window Frame assembly to fit through the opening (at some point, on our Scamp, it didn’t help to keep removing pieces of the stopper because the window panel is eventually stopped from opening by the curve of the window.)  I also had to sand the outer upper and lower left hand (outer) corners of the Interior Window Frame round so the assembly would fit in the window.  It was too tight a fit even after taking these steps, so I needed to remove the outside side piece of pipe foam.  Insulating weather stripping comes with the AC and can be used at the campsite to temporarily fill any gaps

Platform Base
The purpose of the Platform Base is to help support the weight of the AC unit by using a PVC Leg and a PVC Foot to rest on top of the travel trailer bumper (which is welded to the Scamp trailer’s frame).

  1. Platform Base: Cut one 16” wide x 12” deep” x ½”  thick piece (I had Home Depot cut this)
  2. Use the jigsaw and belt sander to slightly round each corner of the Platform Base (for safety)
  3. Cut channels for underneath Platform Base: one 10” x 2.5” x ¾” thick (interior), one 6” x 2.5” x ¾” thick (exterior) (Home Depot can do this)
  4. Insert completed Interior Window Frame over pipe foam and then secure Outer Sandwich Plate to the Interior Sandwich Plate / Interior Window Frame with hex bolts and wing nuts
  5. Place Platform Base on top of the Interior Window Frame (so it doesn’t fall)
  6. Have a partner help position the AC inside the trailer (and someone outside to prevent the AC from falling out just in case) and put the AC on top of the Platform Base and hold the Platform Base in position as the AC back is pushed back inside the Interior Window Frame all the way until it stops (the outer flange protrusions on the AC should stop it from moving back when about a couple of inches of the interior control face is left inside the trailer). Adjust the Platform Base so it comes all the way out to the back end of the AC on the outside, as well as making sure the front AC feet are resting on it.
  7. With the AC nicely in position on the Platform Base, position the Channels (interior and exterior) on each side of the Interior Window Frame so they are against the Interior Window Frame’s bottom walls (inside and outside) and butted up on top against the underside of the Platform Base, not blocking the hex bolt holes, and mark these positions on the underside of the Platform Base (these markings will be where the Channels are glued and then screwed into the Platform Base)
  8. Remove the AC and entire assembly from the trailer
  9. Drill 3/32” pilot holes in the Platform Base (3 for the smaller exterior channel and 5 for the larger interior one, evenly spaced) up from the bottom of the Platform Base (inside the marked areas)
  10. Glue/screw (using #6 x 1” Phillips Flat Head Zinc Plated Wood Screws) both Inside and Outside Channels underneath the Platform Base (using the pilot holes as a guide for screw locations), making sure no channel blocks the hex bolt holes
  11. Place the Platform Base on top of the Interior Window Frame so that it is held in place by the Outer and Inner Channels underneath the platform. It should fit perfectly, with the Channels snugly up against the Interior Window Frame
  12. PVC Platform Base and Foot: Cut three 6” lengths (with saw or PVC cutter) of the 1” PVC and plug two of them into one of the PVC T connectors and also install PVC Caps on each end (and repeat again, but only using one 6” length and cap for the foot)
  13. Set up the AC window mount assembly in the trailer window (with the Platform Base)
  14. Position the PVC under the wood platform so that the PVC Leg (once cut to size) will align the PVC Platform Foot (secured to the bumper with Velcro) with the travel trailer bumper and mark the positions of where the two 2-Hole Pipe Hanger Straps 1” should be mounted (and use the #6 x 3/8” wood screws (4) to mount the PVC Platform Base under the wood platform) (make sure to leave enough space so the wing nuts can still be installed/removed
  15. Cut a section of PVC to length so that the PVC leg will just come down to and rest on the bumper when the PVC Platform Foot is installed (the Platform Base should be fairly level with a slight tilt back so any AC condensation drips outside). This lower section of PVC with the foot can be removed and stored separately for ease of transport when travelling.

Now that all parts have been made and the glue has dried, it’s time to test the system!  Open the rear window, place the pipe foam all around the window, insert the Inner Sandwich Plate/Inner Window Frame into position, insert the bolts, and use wing nuts to secure the Outer Sandwich Plate against the Inner Sandwich Plate/Inner Window Frame.  From the outside rear of the trailer, put the Platform Base in position and then plug the PVC leg into the PVC T Connector on the Platform Base.  Secure the PVC Platform Foot to the trailer’s bumper with a Velcro Strap.  Then, using a helper (to help lift the weight of the AC) inside the trailer, slide the AC into the Interior Frame.  Everything should be very secure and stable.  Add strip insulation as necessary so no sky can be seen when looking at the AC from inside the trailer.  Plug in the AC into the trailer’s 110V outlet (need electric hookups) and let it run to make sure it cools properly.  If everything runs great, remove the AC with a partner, take the assembly apart, and then paint all the wood components (I used glossy White to match our Scamp 13’s glossy white finish).  Now, the only thing left is to plan your summer trips and don’t forget to pack the AC!

Note:  We had the opportunity to use this new AC system in very hot weather (see upcoming Adventure article on the Central Sierra).  The AC performed exceedingly well in over 100 degree weather, chilling down the Scamp so well that blankets were pulled from the closet!

Disclaimer:  You will get the same great Amazon price by clicking on the links here compared to buying directly on Amazon, but by buying here you will also be supporting the continuation of this website as we get a small commission from each sale.  These are products and procedures we use for our own Scamp that we selected and developed from our own research and experiences.  However, we do not endorse any specific product and cannot guarantee that the products we use are exemplary and the procedures we use are complete, accurate, detail the correct recommended procedures, or apply to your model small travel trailer.  It’s always best to double check with your manufacturer or operation manuals to ensure you are doing everything correctly.