I have noticed that my garage, also in Northern VA, never gets to freezing even in the near zero degree days of winter. I keep a water bottle in the garage to see if it freezes just to be sure I will not have any frozen pipes in the insulated ceiling. One thing you could do is put a small electric heater in the garage until time to move it into the house. Just make sure it is not near anything combustible and I would not run it on full blast. Also, keep the garage doors closed as much as possible.