Our cat gets car sick every time we take him with us, anywhere. It's very frustrating, because we want him with us. At first, we had 2 cats and each one was in their own carrier. One cat did fine, the second panicked so much, he got sick every time (both ends). No fun at all when you can't just pull over anywhere to clean up a mess.
We later found putting both cats together in the same carrier took care of the problem. Until the 2nd cat died and we were down to only 1 cat.
For a while, we stopped taking the cat with us. Then one day we let him ride (free range) in the camper. He did fine, several trips this way. Then one day, he got sick. What a mess!
So we had to find another alternative way to transport him.
An idea was born and it's worked great ever since.
That cat rides in the shower with his litter box. We put a towel on the floor of the shower and close cat and litter pan in. The cat uses the liter pan, often just lays down in it. (weird I know). But at least, we've never found vomit or poo or pee on the towel. It must be working! He seems to like the confined space.
Now, the last few times we traveled, we discovered that if we put him in the camper shower and lock him in for about the first 45 minutes of the trip, then bring him into the cab of the truck, and sits on the passenger's lap, he's perfectly content. This has now become our best way to transport him. If he gets sick, he always does it in the first 10 minutes of travel. So in the shower, if he did get sick, it's easy to clean up, and he has his litter box.
This works very, very well for us now. I have a wireless thermometer we put in the camper bathroom too. And in the warm weather we monitor the temperature pretty close when driving. When temps get to 90 degrees, we bring him into the cab of the truck. This is how we discovered, after he has his "round" of getting sick in the shower or uses the litter pan, it's out of his system, and then rides in the cab pretty good But he still freaks out if he's put in a carrier. We just can't do that any more. It's a disaster waiting to happen.