Hey. I wanted to share an idea I'll be pursuing to not use the car battery for heat. Generally I am getting a personal far infrared heater such as the ones listed here: https://www.ebay.com/itm/Desk-Panel-Hea ... b852939352
And plug it in to a portable power bank such as the ones listed at www.goalzero.com.
It's a good way to use energy efficient heat independent of the car itself and utilize a battery independent of the car. Hope this helps someone else.