Wallace, I have not used "clear" powder coat, just a silver like you. The powder coater I had offered a myriad of colors and blends, and he did a lot of custom car work--but is no longer in business. I did find a power coater here in NC now, with a good reputation.
TJ, an easy way to clean aluminum is use an "aluminum brightener"; these are a variety of chemical compounds that use Ammonium Biflouride or Hydroflouric Acid combined with other acids and detergents.Due to their hazardous properties they are getting harder to find. I do know that Kleen Rite Corporation makes one called Klean Wall, that has the right acids and detergents. There use to be some available as wheel cleaners over the counter in auto parts stores, you may have to look around. They work exceedingly well on aluminum usually with no effort other than spray, wait, and hose off.
If you find one it probably is going to have some combo of acids, so be very careful in use.