It simply is rarely safe to sleep in a car. And where would you park? There are very few places in CA where you can legally park overnight. Campgrounds would really be your best bet. Neither is sleeping in a car particularly comfortable. You do not get proper rest to have you fresh for the next day's travel. Why not get onto Craig's list now, and start looking for a couple of basic sleeping bags, a two or three person tent and some self inflating mattresses. (These insulate as well as affording a degree of comfort.) That's about all you need, unless you want to cook your own meals.

Lifey