Styrofoam may not be the safest material to use in our vivariums. See the following thread:
This is a pretty old thread that I managed to find, but I seem to remember other threads more recently still referring to sytrofoam as something to be avoided. I seem to remember a different thread that said that other kinds of foam (the pink or blue stuff?) might be safer. I'm no chemist, so I don't know the difference in the different foam products. I am also skeptical that styrofoam could be completely sealed that it can't interact with the rest of the viv at some point. I would do a bit more research before using styrofoam.