That is why I have decided against using the plasti dip. When I made my first suit, I did not use plasti dip and when I painted my armor, I just used acrylic paint. I had no problems with anything. I even sprayed on a couple light layers of clear coat afterwards and it turned out just fine.
When I started on my Hayabusa awhile back, I made one of the thighs and sprayed plasti dip on it. It started to come apart at the seams where I glued it and and I now have to redo the whole thing in order for it to look as good as I want it. XD
It seems like you DON'T HAVE TO use the stuff, however, it might depend on what kind of paint you are using. If using spray paint, you may want to seal the foam. If you are using acrylic paint or even airbrush, you might be able to get away without using the plasti dip. You will STILL want to paint a couple layers of black over everything in order to help make the actual color you want to make your armor stand out more. That is what I did with my first suit. I did 2 coats of black paint, of course allowed it to dry between applications, then I started to paint it the final color.
My suit looked just fine in the end:
I have come across other people who had the same problem.......pieces seperating after using the plasti dip. :\
Well, that's about all the advice I can give.