This is a sober mainboard cover with open ends. It makes a sort of tunnel so the fan can do its job. I made a seperate fan-holder earlier, but with some modifications this part could easily be merged with this cover to make one object. This part also covers the row power contacts on the power supply.
The cover snaps on the mainboard, and has one bolt to mount it on the free hole in the power supply.
See Thingiverse: https://www.thingiverse.com/thing:904477