I bought a cheap 6 HU 19" Rack Enclosure for Networkequipment that came without the brush dustcovers to help guide the cables through the top or bottom.

I created this dustcover which can be printed on a >= 300mmx300mm printbed and can route up to 5 cables to the outside, which should be enough for most use cases. Cables can be fixed with cable ties through the holes and there are additional breakout plates which can be added in the slicer to help printing without supports and keep the holes closed until you need them.

Print settings:

Material: PETG/PLA+/ABS
Layer Height: 0.2mm
Walls: 5
Infill: Grid, 15%