I tried some of the other coolers available on Printables and the other place but none really felt like they did the job properly.
I have access to a 3d scanner and so I took a scan of the Mini 3 Pro in the closed position and then made a duct system that fits perfectly over the air vents and clips to the arms.
You will need an 80mm fan and 4 M3 bolts to mount the fan to the duct.
Prints with no supports if oriented upside down.