Make sure well primed (ours is epoxy), and then use a proprietary A/F intended specifically for Aluminium - we use Sikkens, but International do a compatible system as well, and I presume other do as well. I honestly cant remember the precise details (the yard order 10 litres every Christmas to ensure it's on the shelf for the spring refit). If you need the precise details I can get that from the left overs in the garage.
Several manufacturers make suitable a/f. International's Trilux (not greatly more use than nothing in my 1 year+ of using it), international also do a teflon based one (with lttle/no actual antifouling stuff...more a v.slippy coating) & there is/was Raffaello Bianca from Veneziani (data sheet <A target="_blank" HREF=http://www.boatpaint.co.uk/acatalog/Act_raffellob.htm>here</A> which is s'posed to be great, but I couldn't get hold of any in time last year due to uk supply prob's.
the boatpaint homepage is a handy list of manufacturers/products....you're meant to use a a/f with no copper or copper oxide....(copper cyan...?? is used in trilux but this is OK it seems). Whether or not it makes much odds using "unsuitable" paint if the bottom's primed/painted first is another matter