This will be a very different post for me. I am part of a Lazy Daze RV Users group. Recently, the subject of insulating the cab area from the back of the RV came up. I commented that I had made a foam bulkhead to provide insulation. That spurred questions and requests for photos. My blog is perhaps the best way for me to post the requested information. For those who "tune in" for my scenery photography, there is more to come, but this post won't be for you.
The basic idea is to provide both an air and a thermal barrier between the cab and the back of an RV. Materials used by others have included blankets, quilts and comforters, as well as cardboard and a material called reflectex. I went with rigid closed cell foam.
You can get rigid foam insulation (closed cell, not the stuff with crumbly bits of styrofoam) in 1, 1.5 or 2 inch thickness, 2' by 8' sheets. Get the kind with a tongue and groove edge treatment so that a good seal between adjoining boards can be obtained. I did mine in 1". (Note - I have kept these photos at full size so details can be viewed if desired. Just click on the photo, then copy and save it to your computer.)
I did the same with a second piece sitting on top of the base. That left about 4 or 5 inches remaining at the top. I glued a third piece to the top of the second piece. I then fine-cut the upper assembly consisting of the second and third pieces about 1/8 inch UNDERSIZE. I trimmed the top and sides of the upper assembly with 3/4" foam pipe insulation, which I held in place with a strip of 3/4" 3M VHB tape placed along the edge of the assembly.
In the photo below, the upper section is resting on the back of the dinette seat, preparatory to matching to the lower section.
I now have two pieces of foam board which travel above the cab and take about 2 minutes for me to wedge into the opening to the cab, completely sealing it. For a color match, I painted the blue insulating foam board with a tan acrylic paint. With the two pieces assembled and wedged in place, a full seal is obtained.
Were I to do it again, I would use two inch rigid foam with a reflective surface. The reinforcing would be 1/2 inch wood, 3" wide rather than foam, with clips to lock the lower board in place. Still, this does a great job, takes me all of 2 minutes to install or remove, and can travel either in the over-cab area as I do, or on end in the space behind the front cab seats.