We do the same thing as n7bsn. We have two dogs in car safety harnesses that are separated by our cat carrier which is in the middle of the back seat of our supercab. We don't have much problem with ours as far as bathroom breaks. We stop every 4 hours for about 15 mins and put the cats in the 5th wheel with access to their litter box and then we walk the dogs. After dog walk, we get the cats from the 5th wheel and then re-crate them in the truck. Really, it is very rare for the cats to have to use the litter box in transit. We "broke" our cats and dogs to the car by taking them on short drive around the neighborhood with lots of positive reinforcement before our first camping trip. We do have towels in both cat carriers as one of our cats loves to get under the towel and sleep. Actually, all our pets tend to sleep while we are underway.