12 volt blanket/throw for small teardrops
12 volt blankets are often better than a heater. Many look alike. Mine shuts off by itself in 30 or 45 minutes, and it is different than the one listed, which says it stays warm until you unplug it. If one has a blanket on top, it will hold the heat in quite a while, but I usually turn it on three times a night, depending on how cold.
A throw is a good size for me because the dog likes it cool on his side.
I tried one that was about half the size, but sent it back because quite useless.
I have plugged mine into a Jackery 500, and with it being on just a couple hours a night, it doesn't use much power.