Most paint with "poxy" in the name aren't epoxy. It's just marketing BS.
Sand off the gloss and I bet most any kind of paint would stick just fine.
Try a little test a area. Paint it, let the paint dry thoroughly then make several cris-cross scratches with a razor blade. Stick on a piece of scotch tape and pull it off. If the paint doesn't come off you are good to go.
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Fiberglass RV