For your 12" x 35" Tuff End Buoy you will need the Taylor Made Boat Fender Cover for 12" Diameter Tuff End Round Fenders - Black Acrylic # 3695200B which is designed for 12" diameter Tuff End Buoys, and will the draw-string will keep it snug to your buoy.
I included a video of the # 3695200B for you to take a look at. view full answer...