my recommendation is 1 quarter of a 10 mg valium every 8 hours for each , double check dosage with a vet but ithink that is it, do not travel with them un doped, if one gets out undoped you will be looking for that cat for hours, i would also recommend individual boxes for them or two to a box, like wood and wire or plastic boxes not cardboard, hey you are real adventurous 4 cats 1400 miles, you rock baby

Earplugs?

Have you tried taking your cats on short trips first?

I have two - one HATES the car (female), the other loves it (male). He actually sits in the back seat like a good little boy. We got him trained to like it by going on very short trips with rewards (like vanilla soft serve!).

For the other... she's just mouthy in the car. I try to just put up with the constant mewling for hours... also, I don't let her have food or water for about, four hours before or so. That way the awful pee-demons don't come to my backseat. ^^;;;

If they are really bad, kitty valium like the others said is a great idea. Always talk to your vet first, of course.

Good luck!

EI moved from Arizona to Minnesota with two cats in a minivan. They get along well, so I just put them in one German Shepherd-sized carrier with a covered litterbox. Rather than getting a sedative from the vet, I gave them Rescue Remedy, which helped a lot. Do NOT, repeat, do NOT let them out of the carrier when the car doors are open. I had the brilliant idea of putting them on harnesses and leashes to let them stretch their legs at a rest area. Suddenly this family with little kids came along, and the kids started yelling, "Kitties!" and running towards us. One of my cats panicked, ran to the end of the leash, and flipped out. All out panick, flip-flop, up-down-sideways, until the harness gave out. She took off running toward the highway. Fortunately she was headed past a really alert guy who blocked her path, so she turned around and was headed toward a corn field, but some other folks saw her, and they formed a circle around her to block her, until I could catch up with her. I would hate for you to have a close call like that - or worse, that if it happened to one of your cats, no one would be able to help you, and you would lose your cat.