Love the original Modern Gridfinity Case by Matthew. However, I noted some issues and things I wanted to improve.

First, a link to my source model. Modified from the original in Onshape, making an account is currently free and will allow you to export whatever configurations you want. I've only exported a 5x5 case with window and my pins mods for this posting. 

Pictured bins are via PRED.

Latch Pins - 2MM x 30MM dowel pins

First, the original box gets torn up where the latches clip to the lid after extended use. So I added a pocket to push in a pin. Now the latches engage with a pieces of smooth metal rather than a thin piece of plastic. This also transfers the wear to the latch, rather than the lid (which I rather not have to change out later). I've been using these for like 6 months and they've held up well. I've designed for a 2x30mm pin to be inserted. Print the lid first, then insert them afterward. They are a tight fit and I found a pin punch helps tremendously. Alternatively, you can just use another pin to push them in.

Side Pins - 2MM x 50MM dowel pins

I also added some side pins that allow you to stack boxes and hold them together. I've made these 50mm with an exposed section of 32mm. This means you should be able to pass 1.25" wide nylon webbing through just barely. Alternatively, 1" webbing has plenty of room.

I'm currently working on some simple plastic clips to join boxes, but I'm not quite happy with them yet.

General Assembly Instructions

Please refer to the excellent instructions written on the original file by Matthew. And of course go give his model some love on Printables.