When we drive from West-Central Alabama to Northeast Indiana to visit family, it is 650 miles and takes us about 11 hours depending on road construction and how much we stop. Less when it was just the two of us with Tsu, more with the three kids! We usually don't stop overnight, but we do have large cities to stop in about every two hours. Seldom do we have to stop that often.
I second the water idea. I would take a few gallons of water from home so changing water along the way doesn't upset his tummy, not to mention in case traffic is bad. There are travel water bowls that don't spill too. I would also take 2-3 boxes or packages of his favorite yummies or things to chew on (kongs, pig ears, bully sticks, etc.) Tsu likes McD's plain cheeseburgers.

Maybe a blanket, stuffy or toy that smells like home?
I would give yourself at least 4 days one way (that would be 550 miles a day-ten hours @ 55 mph). Just suggestions but I hope it helps!