Water marks on Mill finish trailer

[Sherman]

Does any one have any ideas on how to keep Mill finish sides on trailers clean from water marking? Typically the Mill finish will turn black and the resulting stain is very difficult if even possible to remove. Any recommendations?

 

[Prairie Dog]

Black streak remover or car polish will remove the stains but it's a PIA. I thought I'd get away from the black stuff with my new rubber roofed, all fiberglass trailer but I've had no such luck.

I think some of it is caused by the roof getting dirty so I guess I'll have to wash that from time to time too.