I painted the roof of my work trailer in the Spring.......which happens to be aluminum also!
I thoroughly cleaned it with soap/water and a scrub brush, then applied a self-etching primer specifically for aluminum.
I used a 2-part epoxy marine white from Inter-Lux for the top coat and rolled it on (as per the detailed instruction that boat-doc posted a while ago.
It came out great and looks just like it was sprayed on.......smooth, shiney.....NICE!!!