PUPPY!!!!!!!

Sounds like you're doing the most important thing, which is getting him used to the car.

Have you heard of the magic blanket technique for getting dogs to settle? It seems to be the hot thing in dog training at the moment, and might be useful for you if you have to leave him in other places like a sitter's house, or if you take him with you to a cafe or restaurant and just want him to hang out and be happy without your constant attention.