As long as you are keeping the car warm, you should have no problems. Keep an eye out for any direct sunlight on the cage as it can cause the temperature to skyrocket up. I would put him in a pillow case inside a small rubbermaid, put him on the floor of the front seat ( passenger side ), and cover the rubbermaid with a blanket or towel. When you stop for gas, food, or a bathroom break check on him and make sure he is doing ok. If you have an digital thermometer, you might want to take it with you to keep an eye on the temps.