I had an issue one of the first times I traveled with my sportube 3. The case was open on the belt at MCO arrivals because they didn't put the clevis pin in, fortunately nothing was missing.
Since then I put a bungee cord and carabiner on the female end of the tube with a small D ring through one of the holes on the male end. Pretty much fool proof and never an issue since. Now i have both the carabiner holding the case together and the pin (also now tied on with string so it wont be lost).
One key with the tube is to not have any loose items in it so TSA can pack it back easily. Most of them are used to these types of tubes for a variety of items, not just skis. I pack the ski, with vest, rope, gloves, bungee'd around the ski and a small bag with other stuff inside the tube.
When I get to the rental car, the ski comes out and the tube slides into itself, taking up little space and all my gear goes into the 1/2 tube
its always a "ski" never a waterski. As has been stated without a hardcase, you can't claim any damage with most airlines.