Keep the door locks from freezing.
One or two tips.
Squirt lock de-icer or glycerine into the locks to keep them from freezing. To open a frozen lock, try heating the key before inserting it.
A really quick and nasty one. If you have masking tape, just cover the lock the night before.
Just while I think of it, smear your car key with petroleum jelly
and insert it to coat the lock. This should stop it from freezing.
For the car door. I would dry the door and put car wax to the inside metal. This can reduce the car door from freezing shut.
Hope that helps.