When Miko was a pup, he got carsick all the time...I could tell when he was about to vomit because he would start salivating meaning that he was stressed and not feeling well...But we started getting him used to being in a car since we travel so much. Little by little we would take longer car rides.
One thing that helps BIG time is putting the a/c in his face. Also, getting him to lay down.
Now, we have absolutely no problems
He loves car rides now!