We have a full time cat. The secret to traveling with a cat is to have their litter box accessible at all times as well as maybe their food and water.
Our cat usually sits between us in the front bench seat of the truck, sleeping by resting on either of us.
I have created a "cat tunnel" between the truck camper interior and the cab of the truck. Lucky cat doesn't even need to go outside to get up front like we have to. Lol
While traveling the cat mostly just sleeps between us on the front seat of the truck. Sometimes he needs a bathroom break. If he does, he just gets up and walks back to his litter box to use it while we're going full speed down the highway.