Aftermath

After thinking about the model overnight I realised the reason it didn't work is because on my model I used hinged joints (wire ties) to join everything together but in reality my design uses rigid joints (wooden blocks and bolts) to join the components together.

I have to be careful to make sure the joints are as rigid as possible so I have tweaked my design a bit as shown below. I am making the wooden block bigger so it goes inside the tube and keeps everything in place.

Also, after making the model I realised that the paper tube in this particular design is 3300mm long. Other designs are a similar length. I know that the tubes are very good in compression and the metal bolts in tension, which is how I have designed this, but I'm not sure how it would go at this length. I will look at this a bit more tonight after work (I'm running late now...)