My first attempt at making a tank for LEU TreeHugger was by making a core from polyester foam, covered in clear packing tape. I used vinylester resin and fiberglass cloth. The vinylester resin fumes apparently permeated the packing tape and started to attack the foam, which ruined that attempt. Next, I used urethane foam, vinylester, FG cloth. I troweled silicon caulk over the foam, with the experience that nothing sticks to silicon caulk. That worked, but it was a chore to get the foam out of the cured fiberglass tank. That tank worked, but we found "gunk" in the carb, thinking it was from the tank. Later we think the gunk was from tube fitting sealant. Anyway, I made a welded aluminum tank, which has proven to work great. I don't have the numbers with me, but the FG tank was only a couple ounces heavier than the alum tank. Here is a pic of the foam being removed from the FG tank.
Pappy, I think your approach will work just fine. I don't think cardboard will be affected by vinylester fumes, if they get through the tape. And, I like your idea of putting the tank in the center section.
