RE: Shaft Coupler - Good/Bad Idea ?
JeffH and DaddySam have the right idea...solid rod or welded horns...double the servos if need be...the elevator is the easiest control horn to hide. As long as you have clearance for the horn to move inside the fuse. Don't worry about adjustment...set the horn 90 degrees to the L bend in the rod and make your adjustments at the servo end using threaded couplings if you must...you'll be more likely to be looking inside the fuse there for inspection and service of other things. I think everyone is saying the same thing though... stay away from a friction fit clamp especially in an area that may be hard to inspect...if those bolts loosen from vibration or the clamp spins from too much torque or because the material under the clamp compresses, you will have zero elevator control...and while any control surface failure can put you into the ground...the elevator would put you there the fastest IMHO.
Rick