This is a remix of the great print by lrpena here: https://www.thingiverse.com/thing:2887348
No complaints about that file, it's great: it provides a perfect, snug fit for your Raspberry Pi 3 with style and good ventilation.

I wanted a way to mount this without hardware, and without using those little "T-nuts". This is my solution: this print mounts into the aluminum extrusion grooves of the Ender 3 or 3 pro, no additional hardware, no t-nuts required.

To install: take out the 3 screws in the box holding the Ender 3's main board, slide the end-cap out of the way, slip this print in the front and then replace the 3 screws.

Hope this proves useful to people. Enjoy.