The only thing that helped Jo is a prescription from the vet called Mechlazine (sp?). Jo is almost 28 months old and he has not outgrown it...he gets nervous if you even get him near the car. Riley used to get carsick but he's doing much better and I think he will outgrow it.
There was also a new medication just approved for dogs that get carsick but you'd have to search to find the thread. I'm going to find it again and ask my vet about it for Jo...I can't even get him a few blocks from home to the vet without him getting sick.