A rear mounted electronics case for the  Ender 3. At the back, there is room to mount a Raspberry Pi, fan, buck converter and two relays on the left. On the right, either the standard board with four TL smoothers or an MKS Gen L or SKR1.3.
This design is modular, neat, quiet and offers better cable management than the factory design. Rear access is achieved with one bolt per side, without the need to turn the printer on its side. There's also enough room for other stepper motor drivers with large heat sinks if using an upgrade board.
UPDATE: STEP files added. Already some great remixes. Also, I've run some 14 hour prints with the Noctua 40x10mm fan with no stepper driver overheating or layer shifts.
UPDATE: 29/6/20 - Right hand case piece added to suit SKR mini E3, TH3D EZboard Lite or standard board when TL smoothers are not in use. The mounts for those are removed and the mainboard mount shifted right to make access a little easier.
Everything explained here: https://youtu.be/k83M5H796U8