mmm … if the resin you are using is melting your foam, it isn’t epoxy. In all likelihood it’s polyester.
Epoxy will bond to damned near anything but it absolutely doesn’t like to have anything between it and more epoxy. Why are you priming between applications of resin; to visualize the surface?
Here’s a great how-to resource → EpoxyWorks
and some old threads…
for others (and there are a lot) on your URL line type → site:core77.com blue foam (there must be a space between the “m” (in com) and “blue”