I have traveled with cats...Good ones and Bad ones.
Do a trial run first...that way both of you get a feel for the road. DO not open the car door with out the cat being contained somehow....crate,carrier or holding it firmily (not by neck, either). I went to Florida and back with a cat that loved it, loose in car used litter box, etc... And then I have ridden with the cat from H _ _ L, not fun. The vet. can give you something to help calm it down. Also watch the motel room, they are escape artists. SO the Bathroom is a good option. Just chalk this up to...What Parents will do for thier children :-D