Hi Carol,
Did you ever set up a couple inexpensive thermometers to see how cold in cold weather and warm in not so cold weather your garage actually gets? This weekend might be your ''last chance'' for 2017-2018 winter to find out how much warmer than outside your garage actually stays. In about a week, weather is supposed to warm again.
For all new to bonsai, knowing the temperature range of your winter storage is really helpful in planning what you can grow.
I winter my 2 crab apples by setting them on the ground, under a bench, no added protection from outdoor temperatures. They are in nursery pots, 2 gallon and 5 gallon. So they do have some thermal mass, but after a week of below zero, I am certain the roots are below zero. 5 years now, through -17 F (roughly -35 C) they have done well. In a fancy ceramic bonsai pot, I would protect them, more to protect the pot than to protect the tree.
As I think about it, of all my flowering trees, the crab apples have been very reliable, blooming every year, even though they are ''just'' in early phases of training. Really a good dependable bloomer.
Leo