The bad news is that aluminum WILL RUST! The good news is that the rust closes out the aluminum surface protecting it from further rust, but then the additional bad news is that it not very cosmetically appealing.

I have an ALL aluminum Airstream travel trailer which has a special clear coat covering it. Where the clear coat is compromised it will start to corrode (just another word for rust/oxidation) exibiting as a white-ish raised area. Unless the running boards have been protected by some type of clear coat you will constantly have to keep them waxed or use some metal polish to control the corrosion.

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A good pessimist is never dissapointed!