LOL I'm paint mine as we speak!
Just get some Krylon Plastic Paint, then no primer is required. Also pick up a can of Krylon Clear Coat (Satin is the recommended finish for trim). If you dont it will get scratched up super easy and most likely end of peeling off after awhile. Just get your trim, secure it down somehow cause it likes to "blow" away from the paint. Then it gets all messy. So then just hold the can about 12 inches away, and spray up and down slowly and smoothly. NEVER! go heavy on the paint.. if it's too thick your screwed. you MUST wait t apply the clear coat to the paint after the paint is dry.. or else it will turn a odd foggy white... also for your first clear coat, hold the can about 15 inches away and apply one THIN coat, then do the same for the second coat, then apply the 3rd coat as normal. Like I said I'm not sure why it happens if you apply a normal/thick layer of clear coat on the first try, but your trim will turn frosty white.. just a warning.
Thats pretty much it. But I would wait a day/24 hours for the clear coat to harden. It stays soft before then and if you mess with it you will smudge it around and it will end of looking horrible.