We would recommend cat carriers too. We moved 5 cats and a golden retriever from Connecticut to Seattle Washington. 5 days on the road - everybody had a nice safe cat carrier space and I covered them with a sheet to prevent them from seeing scarey trucks and cars out the windows. Kept the AC on and air flowing so nobody got hot and everybody had water to drink. Not one cat got sick or had an accident in a carrier and they were confined for at least 6 hours a day. Couple of them complained for a while when we started out in the mornings, but then just slept all day after that.
Of course they went a little crazy in the hotel.....but that was just to get the ya-yas out.