I like the concept but my concern is if we do this we will have to have a 6 - 10" block welded to the bottom of the trailer to attach the unit to, other wise if Marshall is towing it with his sprung over 40 the tail end of the trailer is gonna drag all over the trail. In adding this block it would seem it would make the trailer more top heavy and the center of gravity higher and have a greater tendency to tip. The other concern is the spring made out of hollow rubber, do they make a spare incase it breaks on the trail?
Just some thoughts
That height's [edit: see link below for dimensions] not any different than an axle under a leaf pack. (The only thing tighter to the frame would be a torsion axle.) And as Marshall said, the frame could be incorporated. The tongue height can be handled by any truck with an adjustable hitch receiver that will always travel with the trailer. I think its safe to assume that any truck towing the club trailer would be lifted at least 2 inches. The difference can be made up with the adjustable receiver.
That timbren design looks far more reliable than other options to me. Even if the rubber spring fails, the axle won't fall off.
I say go with it.

http://www.timbren.com/images/home/Axle-Less DIMENSIONS.pdf 1200lb axles the center of hub is 2 5/8" below the frame rail. Add a 33" tire, nothing is going to hit that.