If you take them with you, you have to be prepared. Find out which motel chains take pets (Motel 6 does, if you don't mind a "bare bones" stay, and alot of Red Roof Inns do, too), have crates large enough for them to move around in and shield them from the sun shining in the windows. Even in an airconditioned car, if the sun is beating down on them or their crate they can overheat quickly. Get them used to harnesses or be prepared to have them use litter boxes in their crates (which will mean scoops, plastic bags, and lots of air freshener! Although they'll likely hold it until you get a room for the night. If the harnesses are no problem, then be sure and stop every few hours and let them stretch their legs, but only if they are used to their harnesses, because if they struggle they may work loose and escape. The really tricky part is meals, because you won't be able to leave them in the car while you go in somewhere and eat. Even with the windows cracked they will overheat quickly. So you will have to pack lunches and do drive through or only eat once you have a room. Once you have a room, you have to be very careful coming in and out because they may dart out the door. And it's best to crate them up first thing in the morning, because the commotion of packing up may send them under the bed, and you may have a difficult time retrieving them.

Travelling with cats can be done safely, but it does take some advance preparation.