I bought this one for Vinnie. http://dogramp.com/
It has sides and carpet, and depending which one you need/buy, it weighs anywhere from 7-22 pounds. I think mine weighs 20. They are always making new models, so the one I have is similar to what you see on the site. They were super fast and I was very pleased though Vinnie wasn't. I also used it for the two steps off our porch when his back got really bad, so it did come in handy.
Adding: They did not make the triple ramp at the time. If they had, I would have purchased it so there was less of an incline in to the trailblazer. It wasn't bad, and we managed, but as his back got worse, he needed less of an incline. If your vehicle doesn't sit that high in the rear, then double would be fine.