Summary
I made it in openSCAD to be parametric and arranged to fit on the bed of the LS3020 laser cutter.
I have made mine out of 5mm perxpex and it fits together well.
The hole is 100mm, you can work the wire of standard 100mm ducting tube through the hole, and tape in on the inside. There are also some optional 3mm screw holes if you want to attach an adapter of some sort.
The box's fit is tight enough to hold from friction alone, though I have since used some poly cement to fix it and seal it. So far it seems to be working perfectly.