Saw a super setup for a cat near Bend Oregon. The clever fellow had put a cat door inside his rig from inside to one of the storage compartments. When he arrived he would open the storage compartment and remove a collapsible wire frame crate. The lifted door of the storage compartment provided a bit of a roof, and the crate set up tucked in close to the wall of the rig with opening doors on both sides. The cat was free to go from outside in the crate to inside the rig through it's cat door, and the other door to the outside gave it's handlers a chance to offer food and water into the crate.