SJN, a blunt trailing edge is a relatively inexpensive counter to flutter, but as a fixed wing and heli pilot and maintenance engineer I know of other places more effective to look into. My friends also fly turbine jets well into the 200MPH bracket so I use them for confirmation and ideas. To be honest that is where I got the idea for the cockpit hatch.

First and foremost is NO SLOP in the controls or hinges. This is the reason I ate the weight penalty and moved the servo above the tail gear. Other than structural weakness a control surface that has play will inevitably reach resonance at some airspeed and/or engine/airframe induced vibration. If not dampened out it can quickly amplify till destruction. Even if both the stab and control surfaces are extremely rigid, a minor flutter may not be recognizable from the ground, but will play merry hell with the linkage and servo mechanicals.

I see from the pics you have the thicker stab joiners. Sure wish mine came with that mod.