Taken the oppo to reduce the phone-box insert to 11" square, although when I've built something similar at full-scale (albeit stretching only to elbow-height), lesson learned was that it can be wider than it is deep: me like many others being that shape myself. Here it gives those propeller disks all the clearance they need from the superstructure while at the same time looking better proportioned altogether... those holes down the sides are exactly one third (12") in. I packed the voids out too with left-over insulation from a partition wall, as it ups its overall rigidity without increasing its weight unduly.
