Try This: Tiny-Footprint Garden Bench

Make a beautiful, comfortable and waterproof garden bench from recycled plastic and rubber materials.

5. Use a staple gun to tack rubber strips, all going the same direction, underneath the top frame. Double up the material under each staple by putting a small scrap of inner tube under each one. This will make it less likely to tear through the rubber. Stretch the rubber strip across the bench top until it’s very taut, and staple again to the other side.
Susan Wasinger