Removed the cardboard, moved all electrical, water, gas, drain lines at least 2 inches above the bottom of my steel I-beam frame. 2-inch styrofoam with tape, then pole building steel roofing screwed to the bottom of I-Beam with self tapers. Dropped the remote thermostat sensor thru kitchen cabinet to monitor temps in my new basement. Unbelievably warmer. We will snowmobile this Winter in our 3950 Cyclone....but still having probs with the digital thermostat and the wide,wide range of temps. Dometic has NO clue how to solve the problems.
As for SpencerRB. Cut 3/4 inch styrofoam panels and put them on windows from the inside. Helps with both the heat and A/C and the public can NOT see it, but we have the mirrored windows. A little "dark" inside, though.