New mattress tips?

Try www.foambymail.com - they sell all different types/thicknesses of foam. I bought a 5" thick sheet of their Lux foam, used an electric carving knife (their recommendation!) to get the custom fit I needed for our "B" (cheaper to buy the entire sheet than to have them custom cut it...). Added a 1 1/2" thick memory foam topper from good old Wallyworld on-line - makes a VERY comfy bed! As a cover for the mattress, and to keep both pieces together, just use 2 fitted sheets - one on from the bottom, one from the top - "seals" it well! With any foam mattress you shouldn't need to insulate under it - the foam itself is great insulation. If the mattress doesn't fill the cab-over, you may want extra insulation along the exposed sides, etc. ST