I have some (now 6 year old) bubble wrap that I keep in the empty sport tube when not using it. A quick wrap around each pair of skis and I've never had any damage to either the skis, sportube, or other contents.
I also use two ski wraps (provided I can find them at the last packing minute) but the wraps provided work as does cellophane. Better than a few wraps of cellophane is the thicker stuff you can find at any office supply place, even Lowes IIRC. Takes two people to start this type of wrap though.
The locking pin thingie supplied with the sportube disappeared on the first flight 6 years ago. As with docmartin my tube was then unsecure but it was together and everything was in it. I now use a wire type small TSA lock that has survived 4 trips. Haven't found one of those "we looked in here" notes in the tube. I also run a thin zip tie through another pair of holes. I always toss a small pocket knife into my checked bag for the other side.
BTW, to get the family to and from the airport the tube gets strapped and bungied to the roof rack. Poor thing sits in the basement unused most of the year. I go visit it every now and then to let it know it is loved.
Are there any tools you normally carry? I take an multi-allen wrench in the carry-on boot bag and toss a cheap multitool into the check bag.
BTW, we fly Southwest so all this baggage is, at least so far, free.