I used to have a dog that got sick/through up every time
she went for a car ride.
She never was cured, but I she got to the point she
could take a car ride for 30 minutes before getting
sick.
I would start out slow with her, just
take her around the block and slowly work up
to 10 minute rides etc. Once she is able to take
the 10 minute rides add another 10 minutes and see what happens.
Good luck.