Ideally make the tunnel frame up on the floor.. although be aware two people will be required to lift
up onto the two towers. Fix the boards to the tunnel ends using the 45mm screws.
The wider boards are fixed to the top, bottom and sides. The side boards are fixed with 1 x
80mm and 1 x 45mm screw at each end. The smaller boards are fixed on the 4 corner faces.
The 30mm x 65mm rail will need to be re-positioned. It should be 7cm above the tunnel.
