Iam exactly in the same situation as your self, I have a Five Month Whippet Pup, who is a very bad traveller.
The things I have tried are,
Very short journeys to field where I let him run, this is two mins in car from my house, did this for a fortnight fine, then took him eight miles, four there and back.
Didn't work he was sick on return journey.
then tried Johnson travel-eze, gave tablets as directed, again didn't work.
He does not appear to be very anxious, so it could be motion sickness,
I gave him two Ginger Snaps biscuits thirty Mins before journey,
then a ten mile trip to the Sea