With only three bottles to use as raw materials, I was going to have to be careful how I used the stuff. The rocket bottle and the NSA cone each take up a whole bottle so that leaves just one bottle for the fins.
I made the nose according to the NSA design. Using a precious bottle (I would have to drink another 2 litres of expensive lemonade to get a replacement :-), I was particularly careful when I blew out the nose to the almost hemishpere that these bottles go to. I put around 30 holes in the low pressure area as shown in the picture on the right and taped the PTFE sheet into place.
The bottles have three unhelpful ridges spaced equally down the straight side so, having cut the straight section off the bottle and cut down one side to make a flat sheet (as per the instructions on making fins from the side of a bottle) I cut along the middle one, making two roughly equally sized pieces, cut them in half, made a template and cut out four identical fins with tabs, sticking them in place as depicted in the diagram on the left. (The reason for making the ends of the fins round was simply artistic - sticking to the lozenge shape of the profile of the rest of the rocket.)
I filled this to between a third and a quarter full and launched at 100psi. The silver sides made it difficult to see where the water level was but not impossible.
On the launcher, this rocket looked quite good and attracted a lot of attention.