I'd just get a large carrier and not worry about stopping. You can put a small litter try in there with him, but he may be too scared to bother with it. :/
I had a 4/5 hour drive home with my boy too, when I first got him. All I heard were ear piercing yowls THE ENTIRE WAY BACK, but that was the worse of it. Every time I'd pet him he'd purr, but would keep up with that maowing. GAAAAH.
I've also made a cross country trip twice with three cats in tow, and will do it again later this year. Five hours is nothing in comparison to that!
I simply used LARGE carriers (where they really had a lot of room), and bought a lot of towels. If they used the bathroom inside the carrier, I'd stop, throw away the towel, disinfect and dry the carrier if it got dirty at all (while letting the kitty run around the van - with the doors LOCKED!), put in the fresh towel, put kitty back - then went off on my way!
There were only two incidents total between the three cats for the entire last trip. Otherwise they held it til we stopped at a hotel each night. Such good kitties.