I've been content to just plug and unplug my power supply to power up / down my printer but cleaning out a forgotten shelf yesterday turned up a nice rocker switch. After a few minutes in FreeCAD I had a box drawn up for it. The switch sits in a 22 x 38 mm opening and a 50mm cube will just hold the switch, wires, and connectors. The back cover is recessed and requires a smidge of sanding for a tight press fit. The cover and recess are drawn the same size but when printing ends up ever so slightly over extruded.
If anybody wants to print this for themselves, STL files attached.