We travel extensively with our "boys" (15 and 17). They don't go "outside" and home and don't on the road.
I would look at a "solid" cage rather then a fabric one.
Some solutions I have seen:
*A cat kennel that attaches to the outside of the rig that the cat access (when parked) through an open window
*An access via the laundry chute to the basement, then to an attached kennel
*A full-up skirted patio room, sealed, including along the rig.
Never allow them to roam, it isn't home and they will not know where to return to when (NOT if) they get spooked. Every cat owner that I have known that has allowed the cat to wander has lost the cat.