Ditto to raindove. I would definitely crate this dog when in route.
Before resorting to meds I would give him something to gnaw on while traveling only to occupy his busy mind. It sounds like a small dog, so you can find some nice bones at the groc store (knuckle bones or 1/2 knuckle bones) that he'll never get chewed up. Nothing small enough to eat/swallow. It's just to GNAW on for the ride and then taken away until he's back in the crate traveling again. Personally, I'd cut every ounce of fat off the bone so that he doesn't get too much rich stuff off the bone and upset his stomach (or give him nuclear gas). He'll learn to anticipate the reward waiting for him in the crate and it should work well... UNLESS he's a super picky eater and the bone is not the BEST thing in his immediate world.
He sounds anxious, so just try to give him something to think about and/or do while moving. My dogs love their crates. They are rarely crated, but often in their crates with the doors wide open during the day. When asked to load up they race to their crates and pile in with tails wagging. They have learned that the crate means a treat.
Good luck...
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