painting door panels, or fiberglass

I have to redo my door panels in my dually. My dash has been painted and smoothed, my front door panels have been glassed, I need to do the rear ones. On a pair of stock panels, what needs to be done to paint to stick to them. I got a set of panels for the rear and porred resin over it. Next day the stuff realesed and cracked and I chipped off.
Whats the proper way to tackel door panels? If I could find 4 nice like new red ones , I would just put them in.
Heres my interior