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