Custom materials concerns

[Gamera]

Jo,
I've just recently discovered this "custom background and fixtures without the use of rocks" phenomenon. Back in my day of keeping anoles, care books had the warning label "be sure to secure the rocks you put together". Now I'm seeing the use of... foam, poly-everything pretty much. I'm stoked about creating something new, but I am concerned about the long term effects of "any-kind-of"-foam (styrene, GS, HF) being under a basking lamp, or exposed to liquid, even if coated with Perma-crete, clay, or other materials. The same goes for the sealants and other substances used.

Forgive the seemingly bleeding heart, blame it on my being a former OCD'er. If everything's cool though, expect to see what I come up with soon. I'll head out to get some polystyrene whilst you all answer.