You can change any parameter on the drawing that you want to suit your particular requirements. I just copied the perspex design into CAD as that was the simplest way. I'm guessing that they use a 7 mm hole as that works with the waterproof, audio-permeable stickers they used

The hole is 7mm as that is the same as the perspex case design which I copied.

I sourced all my hardware from RS Components. Not the cheapest, but they allow small orders

https://drive.google.com/folderview?id=1VP9_oXd07p7U1Bo6GQuOfzrHAzqOs96f There are a few pictures of them. They are in a wetland.

Hi Axel The gasket seals between the box and the lid. The lid has a recess into which the gasket fits. I didn't bother getting gaskets specifically cut, just bought sheets of the neoprene material and cut them out with an Xactoblade. You will also need the additional hardware that goes with the original perspex laser cut case, the standoffs and machine screws.