Coming from the Great White North freezing locks are an almost every day occurance, often many times a day. THe door locks in my 123 freeze only when there has been sleet or rain followed by serious cold. I carry an aerosol container of lock de-icer in the pocket of each of my coats. They are about the size of a cigarette lighter and cost a couple of bucks.
I find that the freezing problem only happens with the doors not the trunk lock. I keep a small hair drier in the trunk. I use the block heater extension cord from the plug in to power the drier. Its amazing what a human can adapt to, i don't even consider this an inconvenience anymore.