Cats behave a number of different ways. Ours stay in the truck and don't even attempt to get out. We crate them to transport them from our house to the truck or from the truck to the camper.
When we first travelled with them, I made a screen / cage that kept them in the back seat of the truck. They spent the entire trip trying to claw their way through. Then next winter we were going to put them in the RV to travel but when it was time to go it was 20 below and too cold for them back there. So they rode in the truck with no cage. They just went to sleep. Go figure.