You travel in the car with the cat in the carrier. You stop & let the cat relieve itself in the greens at travel stops. Use a leash. In the motel, put familiar bed, food/water bowls, litter box in the bathroom, with the cat loose in the bathroom.
I suggest a drive of 30 min to "test" the cat. If it never calms down, get a tranquilizer from the vet. (Valium or whatever.)