I finally dug up the picture from last month of the items I used to paint my aluminum skins. First, I used Klean-Strip Prep & Etch. I bought this at Lowes for about $10 or so. This stuff will last forever, because you dilute it down per the instructions. I used disposable brushes, covering all surfaces of the skins with the liquid. The aluminum might begin to look slightly "frosted" as the liquid etches into the metal. Sometimes this doesn't happen though.
After that, I primed White colored Rustoleum Clean Metal Primer. This stuff is supposed to stick well to metal. Because it is white, fewer top coats will be required later.
Finally, I painted the skins with Rustoleum Satin White. Be careful when painting with this rattlecan. Other builders and I have noticed that it likes to splatter. Shake it up really well and use it at the correct temperature to avoid problems. I only painted the exterior of the skins. The interior will retain the metal look.