Well, generally you want to apply resin in little bits at a time so it doesn't deform very easily. I don't know what you mean by "foam", but you can carefully measure out some pieces of cardboard to use as supports while you resin.
Hey, I saw you asking about how to use blender and unfold pep files (That wasn't exactly the place to ask, btw).
Weeell, I have no clue how to use blender. Tried it, and got nowhere with it. Instead of blender, I would recommend using Google Sketchup. It's not anywhere near as fancy as Blender, but it's a lot simpler to use, and get's the job done. It's free, self-explanitory, and google has a searchable database of 3d models for it that can be uploaded straight to the program. The lastest version can be downloaded at http://sketchup.google.com/intl/en/download/index.html
Also, you can't use a 3d modeling program for unfolding. You must use Pepakura designer (not viewer, DESIGNER). see post below (message was too long to send in one peice) for more info.
The program itself is free to use, but it requires a password for you to save, and getting a password will cost money. But you can still use it without saving for free. The latest version of Pepakura designer is available at http://www.tamasoft.co.jp/pepakura-en/
Hope that helps! If you have any more questions, send me a message.