With nerves a little frayed from the mission-creep on the weight side of things, I take the decision ti include circular cut-outs in each side of the box supporting the pilot, and this reduces its weight by 25% at a stroke. It is also the oldest trick in the book for people who build aircraft ~ open them and they contain more shear-webs than a spider's backside.
Easiest way to do this I have found is to drill a central hole and drop a bolt through the end of a ruler (which often include a hole for hanging them up), and then drill a second at the required distance. Insert marker pen in the latter and rotate. The pen, not you.
