Sorry, I skimmed to the end. My admiration for an outstanding project. I especially think the hood was a stroke of genius. Can't wait to read it more carefully.
Have you played with temperatures in the tank or in the garage? I don't have access to a calculator, but iirc lowered temperatures in either case should reduce humidity. Maybe you don't want or just can't, but if you reduce it a couple degrees in either case it might have a measurable effect.
As for other choices, yes, I'd be thinking of a fan to draw the air out of the top of the room, or an added dehumidifier. 55% relative humidity isn't yet in mold territory, so you have some margin of error, but condensation as a rule isn't a good thing to have inside any building (other than those designed for it like indoor pools.)
If you end up living with the moisture, I'd consider mold resistant water sealers on the exposed surfaces inside the garage.