We painted our 1969 Bon Voyage three times over the years. Sprayed it ourselves each time. First time we used Krylon exterior gloss enamel over primer, then topcoated the exterior gloss with a quality exterior clear coat. Five layers total. We sanded the aluminum to bare metal over most of the trailer, meticulously cleaned the surface, stripped off as much trim as we could and taped off EVRYTHING else. Took us four days, several gallons of sweat, a case of paint bombs and a dozen abrasive pads. We were very happy with the final results. That paint job lasted 20 years. I really think the key to longevity was the two topcoats clear synthetic varnish. The Bon Voyage looked like new!
Since then we've never had to paint the entire trailer. The gold trim has since been twice painted, and I've redone the front and back. A-frame and bumper twice.
Good luck!
Jim