I've had a puppy for a few months now...a failed foster. He spent the first few months of his life in a crate with no socialization. His first ever car ride was when some stranger grabbed him, wrestle...
at home, we feed our Lhasa in the evening when we eat our supper. so we do the same on the road. we wait until we have stopped before we feed him. otherwise, he gets sick, even from a light snack. you might try training him to a cage and use that as a comfort den while you're on the road. and, as stated, the vet may have something to give him.