There is nothing wrong in the method of driving the rudder direct from the servo output shaft that MR shows on his plans for the Hunter, same for the way the elevators are driven. In fact they both provide slop free linkages, I've put two together now and there is no way I'd mount the servos externally or even buried into the tailplane, absolute sacrelige ! Regarding the supplied single wall pipe, there are many flying and I'm not aware of any issues to date.

Ian B