That aluminum is painted using about the same paint and processes as used on the sides. In other words, nothing special. It may respond well to a good washing and waxing. If you haven't tried that yet, that may prove to be a worthwhile investment for you. You might also look into using articles dealing with using a commercial floor wax called Red Max Pro. Many swear by an occasional coat on their properly prepared roofs.
Not sure where the dealers got the idea of clear coat.
1997 37' HR Endeavor, 275hp Cat, Freightliner
03 CR-V Blue Ox, Ready Brake