[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.