Can't say that I've done it, but in general, when painting aluminum like that, I've sanded it smooth and cleaned out cavities, primed it with a self-etching spray primer, filled any cavities, sanded to shape and feather the fills, primed the filled areas and around them, sanded to feather as needed, scuffed everything iff needed for the top coat,, and then painted with any good paint compatible with the primer, in my case, normally rattle can. Mask really, really well and use drop cloths, fine overapray goes everywhere.