I suggest using very minimal resin on your first couple coats for the pep piece. Waterproofing/sealing isn't going to save you when you're trying to work with paper products, sorry. You could also try building pep files that have built in supports or are broken up (not empty bubbles). But, people like fast and easy, so the majority of pep files and the popular ones are going to be tough to hold shape while resining.
I don't advocate using paper supports in any pep build. Using paper to support paper, even if it is hardened, will only be so reliable. Use something sturdy to support your work.