Following on from Mike's tips on Saturday I have replaced the control snakes with 1.5mm piano wire. Soldered 2mm adaptors on to the horn ends and Z bends at servo arm. Managed to slide a brace along the snake outers down inside the depths of the fuselage (a job I should've done before gluing on the bottom fuselage floor) to stop any flex.
Also for the future "hoolies" built in a ballast box.
Waiting now for a good wind at a decent slope!