I kept some of the plastic trim, mostly around the side windows. I did use some insulation--Reflectix applied to the back of the trim with spray glue. Since Reflectix needs an air gap to properly work, the dead air space seems custom made for this. I think I removed most of the plastic trim from the windows down on the driver's side, since it had a lot of dead space with the rear heater ducts inside. So on that side I have my kitchen cabinet, my bed platform with 3 GSM batteries underneath (the bed it hard against the flat trim on the passenger side). I used fiberglass insulation that was wrapped in a plastic tube of vapor barrier and stuffed it into any space in the van exterior, seems to have worked ok. I have slept inside down to 23°F without using a heater overnight and it only cooled off inside to the upper 30sF.