Insulators in a split backstay

[Renoir]

You might be surprised that you can communicate quite well with no insulator. Place the tuner as close to your RF "ground" wire and one of the backstay chainplates as possible. If the other backstay chainplate is grounded/bonded then remove that connection.

Most tuners will tune to anything yet it is the effective radiated output power that matters. Running a high-voltage wire up to an insulator generated great losses because of coupling between that wire and the rigging it is attempting to bypass so try tuning and communicating without one first. I realize the most installations are not done this way yet that is because of "herd mentality".
Rick