Hi Laam!
Just wanted to chime in... I tried that sealer spray I mentioned...NO DICE. The foam still soaks it up and it actually made my metallic spraypaint on top look more dull. I gave a separate piece a light coat in modge podge and the results were SIGNIFICANTLY better. It even allowed the metallic spraypaint to have a nice almost-reflective shine.
I'm still living at home so plasti-dips and pasti-dip spray or anything super smelly or messy are off limits for me, since you've got a whole bunch of other options though, I'm looking forward to see how your trials go!
These girls used EVA foam and coated them in modge podge and have amazing results.