I needed a 3D printer enclosure to keep it warm so it could print ABS. Thais is the first go at it and it looks like it is working well.
in my opinion construction need rope.
every construction is better constructed from triangle not rectangle.
meybe add a hole for rope and add diagonal of a square of thread/rope. the construction will become more rigid
Rope and triangle bracing may help I s'pose, but the 3D printed corner parts are quite strong enough. I did print them in PolyMax and that is pretty tough.
And making it with braces complicates it a bit. Feel free to mod it to your heart's content :)