Temperature in My Car . . pt. 2

Hi! Just a quick update as to my findings so far on comparison of temperature inside and outside my car. Yesterday morning I took this picture. It was 48*F both inside and outside my car at about 8:00am. This leads me to believe that an unoccupied car is the same temperature inside as the outside weather all night.
Last night we drove around a bit (an hour) with the heat on low then stopped at Bicentennial Park to play Pokémon. After sitting in the car (with the heat and engine off) over half an hour it was still 70*F in the car, but 56*F outside. I am wondering how long an occupied car retains heat overnight without running the engine? I do know that, the night Matt and I did the overnight adventure at Walmart, it was very warm and humid in the car in the morning (5:15am). How much does body heat and proper dress play in homeless surviving in vehicles over the winter?
Just now, as I entered my car on my break, I saw that it was 46*F, overcast and raining outside and only 52*F in the unoccupied car.
Hmmm ..  .
My next experiment will be adding passive solar heat to my car. We'll see what impact that has . .
Stay tuned!!!