The OP said the windows will be rolled up and the doors locked.
But, since it seems bears will break into cars, homes, stores and even police stations looking for food, I guess that means building a concrete bunker with steel reinforced windows and doors.
I live in an area with black bears. I don't know anyone around here who is afraid of them. We respect them, yes, but afraid, no. One neighbor caught a bear digging in her garbage. She ran outside and started hollering at it and throwing gravel at it. It ran away.
Another bear has been coming through my alley frequently. No one is concerned about it.
Another neighbor went behind his shed and came face to face with a black bear. Both the bear and the neighbor were surprised at the encounter. Both turned and ran away.
If the OP is in his/her vehicle with the windows rolled up and doors locked, I don't see any reason for fear. It's not like a bear is going to be a stealthy thief. If it is trying to get in for food, the vehicle is going to be shaking and moving. There is going to be noise. I can't imagine sleeping through this. Yes, it might be a bit disconcerting to wake up to that commotion, but honk the horn, trigger the alarm if the car has one, holler at it, start it up and drive away.
Grizzlies are another story. But we are talking about black bears.
From this site:
https://bear.org/how-dangerous-are-black-bears/
"Black bears have killed 61 people across North America since 1900. This no longer worries me. My chances of being killed by a domestic dog, bees, or lightning are vastly greater. My chances of being murdered are 60,000 times greater. One of the safest places a person can be is in the woods."