Cut 1.5 inch styrofoam for sides of I-beam, then 1.5 inch sheets to sit on bottom edge of Ibeam from side-to-side. Threw the black belly sheets away and used ProPanel II steel roofing with fender washers and self-tapping screws. Removed the spare tire and its frame work to justify the added weight of steel. Roofing weighed less:))))
BUT: on my new Cyclone 3950...had to relocated wiring, water lines, gas lines, etc.etc upwards in order to accommadate the 1.5 sheets across the bottom.
Drilled hole in bottom of kitchen sink and dropped a thermostat sensor so I can monitor the actual temp of my "new basement". It is always8-10 degrees warmer than coach AND my floors are warm. Still NOT happy with my digital thermostat for my furnace. 5-8 degrees drop before furnace decides to "fire up" A true PITA when snowmobiling in MI.