I used mod podge on my craft foam magnum and it seemed to hold up ok, though the paint has worn off on some of the edges. Before asking too many more questions on subjects that have been beaten to death on here, read through all of the forums and see what other people have tried. If you read someone's build thread, they generally remark on what materials they use, and often post updates if a certain method didn't hold up well. Research is your friend!! I don't have a clue how many hours I spent on these boards reading on everyone's techniques and picking up on their tips. By the time I was ready to start my build, I had gathered all the info I needed, and didn't have to ask a single question.
Good luck on your build!