I guess what I'm saying is that helicopters aren't any more failure prone with a fuselage on them than not, they just cost more to fix when they fail.

You're obvoiusly competent with setup and your FAI setup experience will serve you well as must FAI guys I know are very precise and meticulous. Heavy paddles, soft dampeners, and conservative cyclic throws make for a smooth flying, scale looking flight regime.

Building the Trex on glass and making sure the main shaft drops through the bearings when everything is tight, dial indicating the fan/clutch to minimize vibrations, in short, things you very likely already do.

You're obvously concerned about harmonics. Pay attention to the mounting directions and make sure the fuselage is properly braced, make sure the blades arent too tight in the grips so they can find center promptly when powering up and get ready to power swiftly through the spool up resonance that most any machine has.