I used to have a German Shepherd that got carsick like that. I had to stop every 10 or so minutes and get her out then continue on our way. I found a couple things that worked for her. First, I always put her right in front of the air conditioner vent so she always had a breeze in her face. Second, I discovered over time that she did best with a small snack on her stomach, too much and she would heave and too little and she would heave. Finally, I found that ginger snaps helped her to not get nauseous. Ginger is an antinausea food and it works in dogs too. Each of these things helped a little bit, all 3 stopped the problem altogether.
