Heres a pick of a background i just did in a bearded dragon cage, what i did was spray great stuff on to the wood, lightly covered that with tile grout then for paint i just used a rust-o-lium textured spray paint and then sealed that with polyurethane. gave it about a week to cure fully and its now odor free and good to go. Others can correct me if i'm wrong but i believe you can use just about any type of paint as long as you seal it with some type of polyurethane. Once again correct me if im wrong but i believe just about any polyurethane can be used as well as long as you give it enough time to fully cure.

also for added effect i molded little cliffs into the background and then sunk fake plants into the wet great stuff, once i was ready to spray my paint on i wrapped the plants in glad press-n-seal and just spray painted everything... took the press-n-seal off after painting and BOOM! nice painted background with out painting over your plants