Lots of posts here about this topic and as many possible solutions, all with their drawbacks.
Four years ago, I considered the options; as far as I could see the problems were that anodising would mean steel catches would need removal first, as would any seals.
Powder coat, again locks need to be removed as well as seals.
Paint, the surface would need to be treated to accept the coating, this would affect any clear coat.
Powder and paint have the disadvantage of flaking, cracking, scratching in use.
In the end I opted to cover mine with the same type of vinyl that's use for vehicle livery's.
It's just like wall-papering!
The advantage is that the panniers can be returned to original easily, you can change the colour at will and it's easy to maintain/replace as or when it's needed.
I've just recovered the outer panel covering on mine. It was scratched to buggery. The ali beneath was like new. It took me an hour to do both.
Have a read.
http://www.ukgser.com/forums/showthread.php?t=67485
