Yep. I have a ranger on tracks with a catch cover hole in the floor on the passenger side. The 18" is about the perfect length to seal it up. I can find lots of the 9" ones all over but can't locate the 18" one. Probably sitting on a ship waiting to get unloaded.
You could modify a 9" to get by until the 18" are available again. Cut up another 9" to make an extension or find a piece of pipe the right diameter to fit the bottom of the 9". JB Weld plastic bonder has worked really well for me including extreme cold and it's available at all the big boxes. My ice gear sled and generator cover are both patched with JB plastic bonder.