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I think it's too cold for too many nights so you won't be well rested enough to drive during the day. Even though one could bundle the air in the face at night would be unbearable for a Californian.
When living in the East Bay CA I set up tent in the backyard with the kids one winter when they were young and found the air too cold on the face for sleeping. During the day no issues but at night
. The tent being lower could potentially be a safety issue depending where you are parked for the night. Sleeping in the car will be cold also unless you are a tight sleeper and the car is warmed before going down for the evening..