Amusingly when I lived in the bush, AK I never locked my truck either. Partly because I was concerned about the locks freezing (it had happened to a friend) and partially because the neighbor would occasionally sleep in it when he got locked out of his house. We never discussed it, but i figured with the weather some shelter was better than none for him (I assume it was the neighbor, someone for sure would sleep in my truck occasionally).
I also never kept anything worth taking in the truck, naturally. We had plenty of, usually drunk, folks who would steal. One night some of them took my 1 up seat and windshield (of all things) from my snowmachine, yet didnt take the $900 otter sled and probably $500 worth of gas sitting in the sled, thankfully. It just seemed so random.