I was inspired by tollbringer's remix (https://www.thingiverse.com/thing:3843759) to add some fans to the lids of TeachingTech's rear electronics case to keep everything cool.
My specific use case has the stock Ender 3 driver board in the left (when viewed from the front of the printer) compartment (using https://www.thingiverse.com/thing:3731202), and an Orange Pi Zero in the right one (using https://www.thingiverse.com/thing:3794903). These lids are only modified from TeachingTech's original file, so they should fit other compartment remixes as well.
I am also including the 40 mm fan grille that is visible in the pictures. All mounting holes are designed for M3 screws. Using the included fan grille and 10 mm thick fans, 16 mm long screws are a perfect fit.
Update: I slightly modified the lids to fit the Ender 3 Pro. The Pro has a wider Y axis extrusion, so this moves the fans further away from the extrusion so there is no interference between the Y endstop or stepper motor. The thickened region is also moved so it can fit under the extrusion (I also gave it a little more clearance, updating both the Pro and non-pro versions). I don't have a Pro so can not verify that the new parts will fit. Please let me know if they do!
3D Warhorse PLA+
You may need to drill out the fan mounting holes to fit M3 screws. The fans can be installed before sliding the lids on, I used M3x16 mm screws and nuts. The lids will need to be bent slightly when sliding into place so that the nuts fit over the lip of the compartment below.
Left Lid (driver board compartment)
Added a 1.2 mm high raised section to provide support for the 2 fans. Added cutouts and mount point for two 40 mm fans, positioned over the stepper drivers, and away from the Y axis stepper motor.
Right Lid (Raspberry Pi compartment)
Slightly enlarged the power supply cable cutout. Added a 1.2 mm high raised section to provide support for the 2 fans. Added cutouts and mount point for two 40 mm fans, with one positioned directly over the Raspberry/Orange Pi and away from the Y end stop.
The Pro has a wider Y axis extrusion, which moves the Y endstop and stepper motor farther from the center. For the pro version of the lids, the raised sections do not extend as far toward the center, and the fans are moved 10 mm farther away.