Aluminum oxidizes as soon as it is cut with tools/sandpaper. Whatever you do, do it quickly!! You have to have all of your supplies at the ready and your process worked out before you do your final sanding. The sooner you get the coating on the less oxidation you will be trapping under the coating.
If you look at Shine's rebuild thread he coats his with coal tar epoxy immediately after sanding (about halfway down, page 4).

http://www.classicseacraft.com/commu...t=22090&page=4

Please post your process with pictures so that the next guy can learn something.
Good luck!

The 7 P's.