We have two have geriatric cats who first traveled with us in a MH about 3 years ago (they were 12 and 13 years old at the time). They hated the MH. We now have a TT that they seem to be much more comfortable with. The litter pan worked well in the shower in the MH, and now we have it in the TT shower. We use a storage box with a snap on lid, and it works great for traveling. No mess. When at the campsite the lid just stands up on end behind the litter pan. I have found the super-clump litter works best and keeps down the odors as well.
Our cats are microchipped and wear collars with ID tags. They also are in harnesses when we travel. We found if they try to run you have a much better chance of catching them before they get out a door. In the MH we also put a leash on the harnesses and attached the leash to something solid when we were going to be going in and out of the MH door at rest areas, gas stations, parking lots, etc.
We use a Feliway diffuser for a couple of hours prior to travel and then for the first hour or so in the truck (connected to an inverter plugged into the 12V plug in the back seat console. It seems to calm them down.
Now we have a more substantial bedroom door, so we feel more secure and don't put leashes on them (they still travel in a harness). In the truck we use a mesh enclosure made for decks and patios, and it fits nicely on the floor of the truck's back seat. They can move around freely but not get out. Seems to be the ticket for us.
Good luck with your (and DW's 3 cats!)