Johanna, I have always heard that using Ginger (in the form of a pill or ginger snaps) is great for motion sickness for people and dogs. Thankfully mine don't get car sick so I've never tried it, but it might be worth looking into.
When Lilly was a puppy, she threw up every time she got in the car. I bought an expensive liner for the back of my Jeep Grand Cherokee from Cabela's to protect the car and she never threw up again.
Makes sense that the ginger might work since all our lives we have been given ginger ale when we are nauseous.
Hope that will help. I'm excited that you might adopt one of the pups!