It gets quite cold hanging out there on the bed several feet above the ground. Previous owner had 1/4" rigid(ish) foam insulation under one bed - but not the other. I'd like to put some rigid foam insulation under the mattress (BOTH beds). But just how much extra space do I have to work with? I've done some experimenting, and I'm pretty sure I can put 1/2" in there. Can I go 3/4? 1"? Anybody ever done this and know the limit? Thanks!