differential between freezing points of water and water solutions. Never had a problem. You may be overthinking this. Keep in mind that temperature fluctuates hourly. If your garage ends up in the twilight zone between 32 and 28 degrees for an hour or two, the insulation built into the freezer will protect you. And the compressor doesn't shut off at exactly 32 degrees anyway.
You're WAY overthinking this. Just enjoy the energy savings when the weather gets cold.