I spent most of the last year travelling all over the US and Canada with a production show starring 11-13 horses. They travelled in a semi-trailer, and though we stopped to water every four hours, never took them off the truck until we reached their destination. I never once saw a rest stop that provided faicilities for horses, and wouldn't recommend risking handling your horses so near a highway, anyway. There are, however, quite a few horse motels, fairgrounds, and even private homes that welcome horse travelers. Through the internet you should be able to find them. If you find more than one place to stay in some towns, I do recommend keeping the info for at least 2 or 3 with you, because sometimes they don't end up being quite the horsey Hilton you thought. That way if you are uncomfortable with the facilities available, you will easily be able to take your horses somewhere else. Some campgrounds also allow you to camp with your horses, though generally you need your own temporary setup to contain the horses. If you have time and are going to use the campgrounds on your trip, get your horses used to a rope corral ahead of time (I'm sure you already know this stuff). Best wishes!