Hi, I use a primer called Varsity Fast Drying Primer I get at the local Pet Boys auto parts shop just up the road a ways. I pay around $2 a can for it. It comes in a red oxide, light grey and I think also a flat black as well.
I don't noramlly use much PE except on intake screens, but I do like to uses those aluminum barrels and those lovely white metal track links from Friulmodel, plus the resin and plastic after-market parts as well, and have no problems from it at all, yet. It seems to have a very finely ground pigment to it and doesn't give that gritty, out-of-scale appearance that I've gotten from other auto body primers. I most generally let it dry and set for 24 hours before doing anything else to it, but have only let it cure out for a couple of hours and painted over top of it with no ill effects. Have used Polly S, Model Master, and Tamiya paints over it and again, no problems. Of course that doesn't mean that one of these days I won't have problems (probably a goof up on my part), but so far all has been okay.
Take care and good luck, sgirty