Does he freak out in thunderstorms? If so, have you tried a thundershirt?
A friend of mine has a boy that is anxious on car rides too but the thundershirt was great for them. They drove 2 hours one way and was fine.
Of course, everyone is different so if you do decide to give it a go, make sure you try it for a while at first.
__________________ Heather Zeus  | Thalia  |