I had the same problem with Burt. I'm self-employed and, whenever possible, take him with me in the van usually distances between 5-15 miles. I just put up with his spewing till he sorted himself out. I think the less fuss you make about it the less the dog will get stressed when its in the car. He used to get really worried and whine alot for quite a few months, resulting in that horrible familiar smell, but he's perfect now.
Another quick hint, always check they haven't spewed on the handbrake before you park up! :sick: