Years ago I drove my car cross country and picked up four hitchhikers. They were deadheads traveling from one show to the next and their car died.
They had a ferret. It was an amazing animal. Very social, it would sleep in someones lap, play with me while I was driving whatever.
My car had no AC and we were driving across the desert. The animal did fine. Keep him out of the sun and happy, he should be fine. As mentioned earlier, watch out for state and local laws.