Ive done this before.. heres a basic step by step of how I did it. I used dupli color products for this project. It wont come out show quality but its good enough for me.

-wetsand with 400 grit sandpaper and then 900 grit sandpaper until smooth
-clean off surface really good with soap and water and let dry
-spary 2 light coats on the surface with Adhesive Promotor if the lip is made of ABS plastic or Poly Urathene.. use Primer if the lip is Fiberglass
-spray light coats of the color paint.. around 4-6 coats should do it but make sure all the surface is painted
-spray 2 coats of clear coat
-wait a day for the paint to dry and cure or if youre impatient like me slap, that bastard on and enjoy

some tips: Id wait around 10 minutes between coats to become dry or at least a little sticky. Make sure not to spray too much or it will drip. All you need is light wet coats. Make sure you do this where dust wont settle on the wet paint and away from things you dont want overspray to get on. Thats all I can think of right now

Anyone else wanna add anything.. I might be leaving a few good pointers out..