If there is a place near you that will powder coat it, that's the best answer. To get a paint job that will last as long as powder coating you need to use a two part polyurathane. The priming and prep of aluminum to get paint to stick is difficult and expensive.
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Powder coating is much more durable than wet spray on paint.I worked in the auto industry making aluminium rims and all were either powder coated or over coated with powdered clear coat if wet painted. It will suffer the same fate as any other paint if chipped and moisture gets under it. The pre paint preparation is critical to getting a lasting finish.
I'm a big fan of powdercoating. But I haven't seen firsthand how it holds up long term on aluminum in salt spray. Think I'd want a beadblast finish for max tooth.
But - just a week or two ago on Latitude38 there was a recommendation to use Dip-It for just that sort of application. It also gives a rubbery finish and is available in spray can from Home Depot.