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...if the lowest temps you get in there are 10*C, You might get a little condensation, but it will be minimal, even at those relative humidities.
Given your description, I think I'd be more inclined to regularly ventilate the garage, maybe even install a large fan blower in the wall or window, and regularly leave the door open about 6 inches at the bottom, unless you're in a place where you are worried about the people walking past trying to break in.
Those are about the winter weather conditions here where I live in California, and I have a garage full of bikes that do fine.
I do share your concerns about what is happening to that wall where the water is intruding.
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