On a plane of this size there should not be enough force exerted on the ailerons to warrant installing hard points. I too would simply harden the mount area with thin CA. Prior to applying the CA, poke a bunch of tiny holes with a T-pin in the surface directly under the horn to allow the CA to penetrate better. Sand after to smooth the surface prior to covering. Those are some pretty heavy duty horns to use on the ailerons, I would use a lighter standard nylon horn with the back plates.

Pilgrim