In bonsai culture we are told to consider trees in pots at least one zone less hardy than if they were planted in the ground. I keep many of my potted plants in an unheated garage that abuts my home on the north side. This is an excellent location as it does not have a tendency to warm due to sunlight. It also has a gravel floor so humidity is probably higher than if it were concrete.
This location generally hovers between 35-40 degrees during much of the winter, although it does dip lower during really cold snaps. Low temperatures are only part of the equation, drying winds are the real problem and being sheltered as described keeps them out of the wind while still allowing the required chilling.
I let everything (meaning otherwise hardy plants, not tropicals) get a few frosts before I bring them in, this helps to ensure that their dormancy is in full effect for the coming months. I have also learned the hard way not to rush things back outside too early the following spring. It is better to keep them dormant as long as they are happy to do so. This is far better than moving things in at night and out during the day, which is referred to as the bonsai shuffle.
Don't make the mistake of thinking that if your plants are dormant they won't need any water, they will. I still water thoroughly during the winter only much less frequently.
I also keep some things outside all winter. These are on the ground and mulched in well with shredded leaves, essentially the pots are buried. My plants need virtually no attention when handled this way. Occasionally I lose something like this so I keep my better/more delicate plantings In the garage.