Regluar Krylon & their fusion paint on bare plastic WILL craze like no tommorow! Same goes for other paints like Rustoluem, Valsapr, the glossy colorplace colors (flats seem to work a-OK), and etc.
...But if you got a good primer underneath, they work wonders and save you money for colors you could get in bigger amounts (though there's also Automotive paints and many ppl have excellent results with them (i'm yet to try them)
A good cheap primer I would reccomend would be Sears brand "quick & easy" gray primer (can be found at Sears stores, Sears hardware and K-mart); I've put almost every brand paint over it and NEVER had problems with crazing or compatabiltiy issues. At a $1.69 for a 12oz can that lasts a good amount fer what ya get, how could you lose?
Weird thing is, the primer they have is good, but the rest of the colors they have in the line are awful. It's also like that with the wal-mart paints, their primer is no good, but the colors are awesome over the Sears primer.
Warning: if out think you should use brand A's primer with brand A's color, DO NOT use Krylon's, Rustoluem's, and Valspar's primers on bare plastic! From my exprience with them, they CRAZE very BADLY and their "Plastic formulated" stuff is the same thing, only with "Plastic" labeled on the can. Though sometimes I find that if you apply the sears primer first then the other brand primer, not only you avoid crazing but you'll get good coverage and a smooth serface for the next coat to bite onto.
Though i'm not saying the're all bad, But again I find that if you mix and match paints (such as the wal-mart paint over the sears primer trick) that works very well.
I hope you guys find this info helpfull and useable.