The servos mount on the rails. Roll control surfaces are inside the rear fins. The canard fins are the X and Y control surfaces. The TV transmitter, radio receiver, batteries and connectors nestle inside the rails, twist-tied in place. Common rocket and plane model parts are used throughout.
Fins are thin ply.
They are interlocked with each other and the body tube is slit for them, sliding down over them. The base disk and the rails sit firmly on the top of the fins. No force is put on the lower body tube. There is some thrust force on the top body tube during acceleration due to the mass of the camera. The highest voltage needed is the 12 volts for the camera and transmitter.