[offtopic]*sigh* It would be nice to sleep....[/offtopic]
I would be interested in this as well, just for future reference.
Things I do know:
Krylon makes a line of spray cans called "plasticoat" they are specifically designed for use on plastic, fiberglass and other non-metallic surfaces. The stuff is a bit difficult to work with but it does work. I used a little of it back in the day when I thought I was a case-modder.
The body filler might react differently to it though.
To paint fiberglass and plastic in the automotive industry, they indeed do use a special primer. I believe bulldog makes it. The primer is more flexible so it prevents chipping and scratching. There is a special procedure for painting though. Generally you have to spray your paint over it while it's still tacky, but I'm not a body shop guy, so look it up.