Some people say that slowly desensitizing the dog to very short trips several times a day at first and then a few times a week will work and the dog's system learns how to accommodate the motion and sensations of a car ride over time in small sessions.
Some will start out just putting the dog in the car and sitting still in the driveway a few times to help take the excitement out of the process(as some think nerves and anxiety add to the problem) and then back out, drive back into the driveway. Eventually drive a short way up the block and back and repeat that a few times each day. As long as he doesn't get sick, you can keep pushing the envelope with longer trips until he gets sick and then back off with shorter trips.
If none of that works after a couple of months, I would get some nausea medication so as not to stress the dog with feeling so ill during a car ride and come to hate them.
__________________  Jeanie and Tibbe One must do the best one can. You may get some marks for a very imperfect answer: you will certainly get none for leaving the question alone. C. S. Lewis |