My husband made this ramp for Bogie, our 55 pound Basset Hound. He used a 1 x 12 (1 inch thick and 12 inches wide) board he got at Lowes. He covered it with two bath mats(from Wal-Mart with suction cups on back side) that he wrapped around the edges and used screws to hold them on. He put big washers under the screw heads. The bath mats give traction for going up and down. We use it with our Saturn SUV, our Chevy Avalanche, and our RV, also. In the RV we stand it up in the bath with eye screws in the wall and a bungie cord to hold it in place. Works great and isn't heavy. When we have to use leveling blocks at a campsite and the incline is steeper we just grab the traveling/safety harness at the top of his back and help a little. Much cheaper and lighter than those we found for sale. You could cut it to what ever length you need.
