Hope your build is going well Tim. Some updates. There may be some difficulty with part 9, which forms part of the gun slide. On the instructions it tells you to cut out the slots carefully before folding. Here is my solution for this part.
Firstly, refer to the attached PDF. This gives an outline of the scoring, folding and cutting sequence I followed. First picture, part pre-scored, slots cut and folded. You will notice that the inner parts have been folded in and left oversize. These will be trimmed later.
Next, the inside view shows the gluing sequence more clearly.
The tray is then folded and the inside parts glued in. As can be seen the slots are necessary for a clean finish on the inside.
The outside is then trimmed to size. When complete it is glued to part 8.
Stay tuned.