Martyn, currently, and I believe since your problems with the torsion axle, it has been changed. The 3500 pound housing is used for all axles down to 1800, meaning you can order it to the weight you want it, but still have the same spindle, bearings, braking system. Over sprung on any system causes problems.
Last year on the Kokopellie, I though I had destroyed an axle, I caught a huge rock, as big as a man hole cover and about two feet thick. It wedged between the tire (35 inch) the fender and the inner frame. The tire where it contacted the rock was less than 3 inches to the rim. should have blown I think!! Lucked out. But it was a monster job getting it out, and of course on a shelf area. When I got it out, it appeared the axle had bent. The tire was cocked outward in the front about 5-8 degrees. Wasn't anything I could do about it, so pressed on. That evening when we arrived at camp, I was thinking about what I could do to save the tire, went to check it out and alas the wheel was straight and has been ever since. Another 8K. These things are very tough, and I believe if ordered correctly, using correct air pressure for the trail, they work great.
I am not saying other systems do not work as I am well aware that they do. I have researched the problem you guys had. Axle coming out of the housing I believe. I have welded an eyelet or have a bolt on eyelet on each axle perch, so it could be chained, come along or tie down to hold it in. I do that only because of what you have said about your failure. Dexter keeps telling me that it is not possible and there are no concerns. I understand their position, so to be safe that is my preventive measure.
But the US Army, Marine Corps, Navy, Air Force and all NATO forces are moving to this type of axle because of its durability and strength. That gives me even more confidence in them.
Bob