Deal with humidity in Garage with no vapor barrier
I have had great luck at sealing slabs with 2 part epoxy paint, in a garage you don’t want to go cheap or when you drive the car in and park it where the tires are ends up pealing up.

I have painted in summer when the slab was dry enough and eliminated a huge amount of moisture in basements. 
This will help if the source is from the slab if high humidity is from the air a dehumidifier will be needed.
I had a friend use a single part epoxy paint and he had the pealing problem. We stripped the paint and used 2 part and it held up fine.