Rh isn’t so useful unless you include temperature. With both you’ll know how much water is in the air and how much you want to remove or heat to add to avoid dew point condensation.
https://openstax.org/books/college-physics-2e/pages/13-6-humidity-evaporation-and-boiling
Why are you concerned about humidity in the basement? Could you instead seal it off from rest of the structure? Are you storing stuff in there? As others have mentioned it can take a lot of energy to heat and dry out the earth.
If you open that garage door you have hot humid air reaching the cold concrete and the water in the air will condense making everything wet.