If you want it to stay malleable, then your best bet is PVA glue base (50/50 mix with water) of 2-3 thin coats. And then a layer or two of Plastidip. That should get it fairly smooth surface while retaining the bendable foaminess (unless you're looking for the foam texture and in that case, IDK). Then automotive primer and paint.
I used Krylon covermaxx instead of the automotive paint on my cyberman's thighs and it worked fine. No cracking when bent/pushed.