In a garage situation (or even the refrigerator), once the soil is sufficiently dry, put the container(s) in a plastic bag. At least here, our winter relative humidity is always low, say 10-30%. A garage is always warmer than outside, and of course the same amount of water vapor in the outside air brought to a warmer temperature makes the relative humidity even lower. Uncovered pots will continue lose water until tinder dry. We want to have the plants drier, but we don't want to dehydrate them.
Remember, though, that frozen soil always looks dry, whether it is or not. If you are familiar with lifting containers to see how much moisture they hold, this will be a good interpretive gauge. Frozen water weighs the same as water in the liquid state.
