UPDATE 6/1/2019: I pulled my Z motors, motor holders, and X axis off and used a square on my frame and it was almost completely square (about 0.2mm gap 16" up.) I will most likely make some modifications to this design later that also adds a slot on the back screw so that you can make sure you get it aligned correctly.
UPDATE 5/24/2019: Something I'm a little worried about is the back screw pulling down on the case causing some torque on the Z axis. I'm up to suggestions for fixing this. I know that the original Prusa's RAMBo case is only attached to the Z axis. I don't have the PSU attached, so I can't compare it to that, although I'm printing something up now and I do believe the rear/bottom attach point has two slots crossing each other that was probably designed to prevent this possible issue.
UPDATE 5/21/2019: The prints came out great (no perfect, but awesome enough.) I used Atomic CF PETG to print this with, using 0.20mm layer heights. I did use supports for the main box, but only from print bed. I think that the design is almost perfect. It looks like the angle for the lid fan duct is off just so slightly where the top touches the fan housing and the bottom doesn't. If I start getting annoyed by mine, I'm just going to sand it. I will update the files later when I get a chance.
Ocie's Box is awesome for housing the Duet Wifi, so I modified it to fit the i3 Full Bear frame. Unfortunately I did not realize the first one I modified would only fit the MK2/2.5 frame. This remix should fit the MK3 Full Bear Frame. You all are getting the design and source files while I'm printing it up to test it (I'm hoping it works first time, but that rarely happens for me.)
Please feel free to use the Fusion 360 files to modify it to your liking.
You'll notice that I did away with the back hole and changed around some of the chamfers in order to fit a DC-DC SSR that I'll be using to control my MK52 heatbed (I pray it's enough room to hook it all up.)
I've also added more front holes (that face the Z axis and are hidden when the box is installed) to reduce material used and give more options for running wires down the Z axis and into the box (I have no idea what you'd want to run with it, but it's there!)
I've also added the V slot grove mounts on the mounting tabs (two tabs mount to the Z axis and one to the Y axis on the back.) The hole for the Y axis has been moved to line up with it and brought closer to the side so you can get an allen driver in there to install it if you have the board installed already (hopefully ...again, I haven't tested this yet.)
I will post pictures of my print after it's completed, and then once more when I install it.
And thank you Ocie for the awesome design!