I started using an OctoPi 3D printer server with my Ender 3 Pro a while ago. It’s super useful as a remote management tool, but I wasn’t able to find a mounting enclosure for my Raspberry Pi 3+ that met my requirements. I made this one by marrying two two open source designs and tweaking it a few times.
Fun fact about the Ender 3 printer: it can receive power from its USB port, so it’s important to isolate the 5V power signal from the USB cable if you ever plan on turning the main power supply off. Otherwise, the printer circuit board and hot end fan will just stay on all day. I just cut into my cable and crimped on some spade terminals to be able to use the USB cable for communications only.
I started with this Sleeve Case for Raspberry Pi by Walter Hsiao and made some changes to it so that, instead of the face plate snapping in place, it screws in place with 4 size 3-48 x 1/4″ screws, which I had lying around. Then I extracted the clip component from the Ender 3 Cable Chain by johnniewhiskey that I have used previously and that works really well. Put them together and you get a Raspberry Pi case that just snaps into a v-rail.