I would get meds to help. Making him go on car rides and get sick each time is NOT suddenly going to make him like it. If it is anxiety then the meds would allow him to travel without the bad feelings (more relaxed) and eventually may not need anything to travel comfortably. If it is motion sickness, which I believe anything that has eyes and ears can have, then meds again because throwing up every time you get in a car is not going to make him want to go for car rides either. Maybe he will outgrown it as time goes by, maybe not.