There's a need to pass various "things" from outside the enclosure to the inside; specifically the power cable for the printer, the power for the Raspberry Pi (running OctoPrint) and four Bowden tubes to feed the filaments to the extruders. Rather than trying to get the specific requirements for these worked out ahead of time, and risk them being wrong, I had a rectangular gap cut in the back of the case. I then 3D printed pieces to fill this gap with specific holes for my various cables and tubes.

Three pieces are use. The main plate has holes to pass the four bowden tubes, and a circle hole large enough for the power cables plug to pass though. The second pieces is a "lip" which pressed onto the first once it has been position in the case wall. This keeps everything in place without the need for glue. The final piece fits in the circular power hole and has cut-outs just large enough for the printer power cable and the Raspberry Pi power cable. They all fit together nice and tightly and limit unnecessary heat-loss from the enclosure.

The final assembly can be seen above.