If I have to take my dolls in my car with me, I let them sit in the backseats if I'm still in the car. If I have to leave my car AND leave my dolls all by themselves, I lock them in the trunk. I think the trunk tends to be cooler than the body of an automobile, and it's protected from sunlight. Also, it makes it much harder for anyone to break in to steal them. If the weather in your area is very hot, I'd leave my dolls at home because I'd be worried about heat damage.