Relevant story: a few years ago in early winter I was taking a styro box with a few geckos in it to the vet, which is over an hour drive from me. Had a catastrophic breakdown on the way -- the fuel tank let loose from the truck I was driving (I don't recall why I was driving our beater truck). Not only could I not run the heat in the truck, but I didn't want to be part of any flaming vehicle with the leaking fuel situation, so I waited an hour for a ride sitting on the side of the road with my box of geckos. They were fine, but they got quite cold. A few heat packs would have been very helpful.