WD-40 used PREEMPTIVELY works great. Displaces the moisture that can freeze. Nozzle in the key slot and hose it out. Another BIG offender is the door gasket can get wet with melt water, then freeze overnight. Knuckle dragging mouth breathers routinely rip the door handle right off... (they are very tender compared to yesteryear) so if that is encountered, try all the other doors, maybe find one not frozen as bad, or grab the edges of the door with strong (daughters manly bud) fingers and pull while holding the handle unlatched. Also, use dry silicone spray on all the door gaskets BEFORE winter, it will reduce the freezing to a minimum. Your welcome.