I would not rely on heated seats in car to keep it warm. What happens if you have to wait 45 minutes inside somewhere? The bottle will not stay warm enough. One hand warmer on the outside and your ballsack on the other will keep it 100 until the warmer goes out. I was able to keep mine at 100 today for over 2 hours but thankfully I didn't need it.

Edit: You were not watched at quest in 2001. Tech did stand outside but you are never watched unless you are on probation or something else like that.