Start with the short trips.

Tasha, my puppy mill rescue, got car sick when I first got her. She was terrified that something "bad" was going to happen -- AGAIN. So I just kept taking her, going to our fun places: walkies sites! And I would tell her: Going walkies! Go Slater!" "Go Farm Walk!" So she would know which place we were going to.

I also (bad me) let her sit in my lap, and held her up to look out. She was afraid of that as well at the start. Now, she demands my lap and the open window, puts her head out, he hee. She has to settle for 2d behind my Lacey who has always loved the window spot.

Anyway, with rescues, and if you don't know their background, you need to go slowly and talk, talk talk so they know what to expect. At the start, they are just so frightened they won't even hear you, they shut down. But over time they will tune in.

If it really IS motion sickness, sometimes you can work that out as well, doing the repeat short trips for fun things. Only if that doesn't help would I suggest a treatment. There are some "treat" type things which work great for short trips.