If you're buying brand new 2003, You'll be way ahead of the pack in many ways~
First, the top on all newer models are one piece white. The most you'll have to do there is wash it and, enjoy the extra cooling effects..
As for the rest of the outer skin..Time will only tell, as it's now claimed by A/S that the finis on all new A/S are pre-finis (coated, treated by ALCOA..) before the panels arrive at the factory.
I would say this:
Wash your trailer after each trip..Never let the splattered bugs, road tar, etc set up on the skin protective cover for any period of time~!. Washing it with just warm water should do the trick for the most parts. Other tough things, such as tar, oil stains will require a stronger approach. This can be done using use a small amount of kerosene on a rag and, wipe the spots till its clear. (Be careful not to scratch your finis~!)
Walbernize your unit at least twice a year, or more depending on the use. Try to avoid parking under trees of all sorts. Birds, tree sap, etc can be, at times, very difficult to remove once harden.
Just like the clearcoat on your car, the acid can eat thru it, making for the nasties.
Before putting anything on your unit's outer skin..
Word of Caution~!
Always read the label, research the products MSDS sheets..Read the fine prints, avoid like the plague ANYTHING that has ammonia base or acidic agents.
I think you get the general idea..If you ever have a question about the use of any product, this forum is a fantastic place to come with your questions first..
WBCCI 5292 AIR 807
New England Unit