I dont know if you've seen this youtube tutorial yet but it is great for teaching one how to make foam armor using pepakura.
It has 7 parts, I watched the whole thing and I know what to do now I just have to decide what I want to make this year. Halo 4, Reach, remake Classic Cyrax or the new Cyrax. Looks like its a lot faster to build than cardstock, folding, and glue but you do have to modify the pep files too. You still make the helmet out of cardstock and fiberglass it but having the rest of the suit as foam would remove any mobility issues I'm sure.