Sweet, a question I can actually answer.
Ive painted a few sets of rims, and so far they've lasted 3 years without any issues. still look like new! If you want that nice powdercoated look, I use DUPLICOLOR High Heat Engine enamel.
What you have to do, is make the sure the rim is 100% clean, and if there is any rust, or peeling, that its ground off. Then wipe it down quick with paint thinner, mineral spirits, etc. Spray some paint on, (start with extremly light coat, and let each coat dry 15 min before next). Let that cure for as long as possible, then spray with DUPLICOLOR HHEE clear coat, and let it dry.
It will be bulletproof when cured, and every time you wash and wax them after beating them up, you'll be amazed.
My .02cents.