i've heard water down white elmers glue, and spray plasti dip. to be honest i just painted a foamie alien tail whip with nothing and it came out jsut fine. no cracking or anything. And yes i ran around whipping people with it, and still had no cracking or peeling..
I use white glue and sometimes flexible polyester resin coating over foamies - then paint with plasti dip and acrylics.
I still had a lot of trouble with multicolored foamies base colors still showing through after a lot of wear and tear (moving through crowds and tight spaces)- so I switched to purchasing only Brown anb Black Foamies to start with. Avoiding the Yellow, Green, Orange and other bright colored foamies
At least this way when foamie armor innevitably gets scraped, it doesn't show all rainbow bright under the paint scratches.