I crossed the country in a rental moving van with two cats. I had obtained some cat sedatives from the vet before this. Each cat had their own cat carrier box and I put them in the front seat with me, lashed to keep them from moving too much, and facing me so they could see me and I could keep an eye on them. I placed a bath towel in each box that we had slept with for something soft and for some kind of familiar smell.
I gave them water but no food. Turns out they weren’t in the mood to eat anyway.
The first day was pretty quiet, just unhappy faces peering through the mesh.
I stayed in a hotel overnight, the blessing was that the bed wasn’t on legs, it was on a solid box, Otherwise I would’ve been digging them out from under the bed in the morning.
The second day, despite the tranquilizers, they yowled and whined almost constantly.
We took a potty break during the days at a rest stops. I took cut-down cardboard boxes, lined with garbage bags, as a litter boxes so I could pitch the mess easily. I just placed the box on the cab floor, and let them out of their boxes. I kept the truck cab closed up during the whole operation because I have no illusions on how to keep Houdini and her brother contained when they really want to get out.
HTH, Belrix.