Hard water stain
I think I saw the answer to this once, but can't find it now or remember the solution.....When running the rooftop AC, water will trickle off the roof(normal) and run down the side of the coach leavin...
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Just pour some automatic dishwashing liquid right over the stains and let it soak. Then simply spray off, just like a dishwasher would spray your dishes. You may have to repeat a couple times but it will come off. It's made to remove lime and calcium build up (water spots) from dishes. FYI works fantastic on glass shower walls too
