Bob got the Abetta Pathfinder Saddle that is flex tree and it seems to have stopped the back and leg problems of Ghost. The treeless saddle moves around a lot from what I hear.
I figured you'd know about them if anybody did. I hear that a lot of endurance riders use treeless saddles.
The Hilason claims to stay put, even on the most witherless horses. So I don't know. Maybe my friend will buy one and I can try it out.