Well it's not really a cover for the seat, but we use a Snoozer carseat for Katie Scarlett. Of all the things we have bought her, it has been one of the best purchases. She had gotten sick twice in the car before we got the Snoozer. I had her in her carrier each time. Well the first trip and every trip since (which is almost daily) she has been fabulous in the car. No sickness at all. The Snoozer elevates her up so she can see out and I think that helps her. We drive back and forth to see family (a 12 hour drive) quite frequently and she does great in it. And the cover for it is removeable so it can be washed. I'm not sure if it is what you are looking for, but here is the link to the one we got. I got ours in pink vinyl so it can easily be wiped down. I have washed it in the machine one time.
Snoozer Lookout I Pet Car Seat- All Other Fabrics - Snoozer Pet Car Seats - Dog Car Seats
Hope that will help some! Good luck to you!
