We bought a large size dog crate, it is soft sided with bars that are spring loaded that keep it in shape. It fits nicely into the back seat of our pickup and our two cats travel nicely inside it together. We have noticed that one of them doesn't like windy bumpy roads and gets car sick. Went to the Vet and got some cat sized carsick pills give him one and he is lights out for most of our trips. They do wake up when we stop anytime and we make sure we limit our travelling to stops at least every 2 hours. It gives them a chance to take a break as well as me. They might get a little noisy but usually settle down when they realize they are not going to the Vets.
I also made some minor mods to our TT so they can use the litter box in one of the storage areas that we have outside access to. It is the one that goes completely across the front of our TT and is partially under the bed. I made a whole in the panelling the size of an average cat door. One of our cats is a little skidish so often uses it as a hiding place when company arrives. I also divide the space so it keeps the litter contained to a small area as the youngest cat is a real digger.
I wish you good luck and happy trails.
