I had a garage coach and I carried a Mini Cooper, a 427 Cobra, Jeep Wrangler, Porsche 911 race car and a Porsche 996. One at a time. I never once had any smell of gas or any odors in the coach. I had the bed (real queen size)over the hood of the car.
I also had a lift to put the car in.
Send me a Private Message and I will tell you about a project in the works that has everything you would need, Mini, Atv, Queen bed,..