Okay, minor tweaks to the fan-to-toilet adapter:
* cut out part of the mount that interfered with the screw
* increased overall size of the tube that goes into the toilet for a snugger fit -- went from 48mm to 48.4mm and also decreased the inner diameter of the shaft from 44 to 42.4mm (so our wall thickness is increased from 4mm to 6mm, I wanted a little more strength in the wall just in case)
* add another 3mm in length of the tube (doesn't quite clear the top of the screw tab)
It looks like:
