Variation I drew up in F360 from scratch. The slotted bracket is made to accept heat set inserts (M6x0.8x10). 

Printed first trial in PETG 100% infill, feels quite a bit stronger than expected. I'll use this to mount a smaller tail bag (along with two forward fulling straps) when not using my Reckless80 (which has the MM made Gnoblin in stainless steel all parts).  Not using the knob, but made it anyway. It might be able to be remixed to use as a wall mount for the Reckless when not on the bike.