We use the "Safety Seat Support Harness" made by Four Paws that is fleece lined and very wide across the chest and under the belly. Our vet called it "Bogie's skid plate". We got a very heavy duty nylon leash (made for monster dogs) that we use to tether him with in our SUV. We use the tether metal rings (actually retangular shaped) for baby seats in the SUV at the base of the back seat and thread the leash through that and tie it to the length we want and hook it to the harness. He can sit, stand, lay down, and but not move around. When we tried to use the regular seat belt, it was the type that have the shoulder harness and lap belt together, and he couldn't move at all, only sit straight up when belted, and was not a happy traveler.
We also bought some very firm king size pillows, that I covered to match the grey seats, that we stuff along the floor board so he can't nose dive there. I lay a rubber backed rug on the seat for him to lie on, won't slide, and he rides on that and does great.
I'll try to get pictures next time we have him out for a spin.
