One obvious weak link on all the RV horizontal tails are the hinges. They're rod ends, screwed into big nutplates. All of the counterbalance mass is placed outboard on the counterbalance arm. In a situation where flutter dynamic is present, when that outboard mass is resisting motion in the elevator/stabilizer, the first component in the airframe that supports those loads is the outboard elevator hinge. Strengthening this hinge would make the horizontal stab / elevator system stiffer, allowing less flexure at a key point in the load path present in a flutter scenario.
From what I've seen on the rockets, this under designed outboard hinge point has not been improved. Please correct me if this observation is incorrect.
An improvement to the outboard hinge would be to get rid of the rod end and use some kind of solid billet hinge on those outboard locations. Its really not necessary to have adjustability on both hinges (center and outboard). Keeping only the center hinge adjustable still works to align the centers on the elevator hinge axis (edit: although I don't like the rod end hinges at all).
Heavier skins are good, serving to keep a more torsionally stiff elevator and adding resistance to the skin buzzing. (but heavier skins also require more counterbalance mass, adding 2X to the hinge loads I see as problematic in the first place)