Just returned from the Smoky Mountains and while we were there it got pretty cool, even down to 31°. So for a few nights and days we ran the heat. I discovered the closet slide out in the bed room was sweating very bad on the outer wall and the aft wall of the closet. I mean it was a RAIN FOREST type of sweating!
I purchased at a local Lowe's some Styrofoam that was about 13.5" wide X 4' long by 5/8" thick. As you can see in the attachments (pictures) I cut the foam with a razor knife about 1/8"to 3/16" larger then the actual opening
of the wall. In the three compartments (three) I simply forced the foam against the outer wall without gluing. But on the "HANG UP" side of closet
I used a white "LOCTITE" glue with a caulking gun. I cut the foam slightly
oversized for the "HANG UP" side so it would wedge into place. Did not have to apply any foam to the small compartments the shows the "WOOD GRAIN" finish. Apparently the wood grain is double layered which gives enough insulation to prevent sweating. All materials, Bundle of Styrofoam,
glue, caulking gun was less then $15.00.
The RV unit is a ROCKWOOD FIFTH WHEEL.