This I can speak to first-hand, as I have three youngish Japanese maples in pots myself. They spend the winter in my unheated barn (which is well-insulated, however). I roll the potted trees into the barn on a hand truck, and when there are thaws of a prolonged nature midwinter, I check the soil to make sure the plant isn’t ever bone-dry. Last winter I watered them perhaps twice all winter long; mostly they remained frozen. My pots are large…so this provides additional insulation to the root system. I’m attaching a photo so you get the idea of what I mean by large.