The first thing you have to do, and the most important, is get everything down to bare aluminum.You could sand it, scuff it, but the best and easiest way to go is a chemical stripper-go with one of the new ones- non toxic, no fumes and doesn;t burn your hands.They were originally formulated to strip aircraft.Check out the website
www.napierenvironmental.com for a product list and where you can buy it.

There's no point in going to all the trouble and expense of repainting if you haven't prepared the substrate properly, and you can't expect whatever new coating you use to be successful, no matter what brand you use