David,
Mine has a bar that connects with three clasps at the tube and seat and seems pretty stable, although not as rigid as a round tube. I can see the point about stability in a beach launch, but I think I would be O.K. in my tube entering with caution as would be expected of any launch. By the way I have all of July off work and look forward to finding a day to fish with you somewhere. It is a couple months off, but as we get closer lets make a point of getting together.
Dave B.