Duet Wifi controller box attaches to 2020 extrusion

This is a control box for mounting a Duet Wifi board on a 3D printer or other machine that uses 2020 aluminum extrusions.

This originally started out as a remix of Greg24's Duet Wifi mount/cover here:
http://www.thingiverse.com/thing:1920401

The further along I went, the more extensive the modifications I made, and I ran into issues as I converted it from a box with a removable bottom to a box with a removable top instead, and in the end I just started over from scratch. Everything about my box is a little different, including the dimensions, the nature of the holes for the cables coming in, how I mount the board, how I envision the airflow through the box (I have extensive venting on the opposite side from the fans and a solid lid), etc. I also added a mounting rail onto the side of this box that allows it to be screwed down to a 2020 extrusion.

I didn't put any holes into the corner chamfer of the ledge around the top, for securing the lid. This is because I leave it to the