This is going back a ways, but I remember when Bud and Tash were pups I did a fair bit of reading on the subject and it seems to me I remember reading that alot of young puppies get motion sick.

I know if I've had a beer or two too many, it helps to open the window in the cab!! Not sure if that advice transfers to dogs!

I think it's just a matter of getting him used to it slowly with short trips.