First I want to build a large cage for my redtail boa which is about 6' long but like to climb. I would like the dimensions to be roughly 4 1/2' - 5'T x 4'W x 2 1/2' d, made from stained, polyurethaned, oak plywood attached to a frame. I would like to create a fake rock backround on the back and sides of the cage and am looking for ideas to create this. Ideas so far are plaster, but I want it to have a rough,kind of porous edge to it. Is the some kind of foam or maybe I would be able to add something to the plaster to give it a rough surface. I wouprobably paint it grey and add maybe green and black shades to it. What would I seal this mess with? Also would like to add a misting system so it would have to deal with humidity. Thanks for any replies.