You can use a spray on clear urethane.... but as with all clear coats
they dont contain UV inhibiters and the coating will fail after a few
years.

Anytime you disturb the anodized coat on aluminum you risk penetrating
through the anodizing ... and then you either re-anodize or wind up
polishing/cleaning ad infinitum.

In article , Keith
wrote:

Check out:
http://www.shieldproducts.com/
http://www.nyalic.com/