Looking at the details for the gun arm. It is quite complex.
I tried designing them in a 3d package and transferring them to Pepakura but I found the detail was too difficult for me to glue together without it not looking right. A full size version could probably be made much easier.
It was only when I put it on the tube and then I could see that it was off centre and so I started to think is there an easier alternative way to do this?
I started to wrap paper around the tube itself while gluing as I went along. I am not sure how well it will turn out.
I then painted it with white glue
The next step is to fill the angles with some filler,