[carmine]

Hello Maxum.
What Fast says is good way to do.
All i would suggest is start with 400 paper then 800 paper then 1200.
Use a wood block behind the paper to help hold the paper flat against the fins giving you a nice flat fin top not a domed fin top which is what you would get if you use your hand behind the sandpaper.
Most importantly always sand in X patern (change direction after sanding marks all going in same directions).
Use varsol while sanding, helps keep sandpaper from cloging up with aluminum and longer life of sandpaper.

Best Regards Carmine.