
As someone who was incredibly car sick myself as a child I sympathise. I've just had a litter of puppies & had completely different experiences with 2 of them - which might help. The bitch I am keeping myself, so I took her out in the car occasionally from 5 wks old. The first few times, OH drove & she was on my lap. She squirmed a bit, didn't get her own way & went to sleep. Then I put her in a very small cage which just fitted the front seat. She squealed & bellowed for about 5 minutes, then went to sleep. She's now 9 wks, still squeals for a couple of minutes, then sleeps. She has never ever been sick (she probably will be tomorrow having said that.) The dog puppy I sold to someone who lived a long way away, so I took him half way on my own, him in same small cage. He screamed & bellowed, before I'd gone 5 miles he'd been sick, got on the motorway and he decided he had to poo! OMG, had to drive 50 miles before I could stop at a petrol station, buy 2 toilet rolls, clean up sicky, pooey puppy, sicky pooey cage, sicky, pooey car!!! The new owner got hold hold of him & said "Oh you do smell of sick!" - then gave him a great big cuddle!!! He went the rest of the way cuddled in a coat on a knee & just slept all the way.
So, what I am saying is, think you have to take it easy, start off with him on a knee, graduate to being near someone in a cage, to being on a cage on his own in the back. He will grow out of it, but you have to perservere & don't stop taking him in the car. Taking him on a long drive on a motorway may also help - it si stopping & starting & corners that make it worse.