Howard,
the important question is what are you going to put on top of the primer adhesion coat? that more directly influences what you use in reality?>

Howard,
I would use PPG  Acrylic lacquer primer. DZ3 is the Grey if I recall correctly. I think DZ7 is the red oxide but I never liked the red primer. Of course make sure you clean with every possible cleaner you have before you do this to insure the mold release is all gonzo! I would also recommend sanding with something in the 220 or 240 range prior to spraying your primer. Lacquer doesn't have the same bond as urethane primers and the extra mechanical tooth will help since the resin you are undoubtedly using is rather lacking in porosity. Also, lay on thinner coats as oppsed to a fewer number of thick coats. This will really help the primer to be able to breath and dry sooner. In years gone by,, back in the day, i always thought fewer coats of really syrup thick primer would be better but it really  will haunt you since it takes literaly forever to dry........
good luck Howard, hope this helps!?

You could also use a catalyzed, urethane based primer like K-36. Dope seems to stick to it fine. You just have to be careful about sanding through it. But adhesion wouldn't be a problem, I don't think.

I have painted the plastic parts on my motorcycle, 26 of them to be exact. I used an adhesion promoter called "Bulldog" which I bought at the auto paint store. It comes in a spray can and is made specifically for the purpose you state.