Alright. Here it is at long last lol.
U-Box Final with Heatsink.stl (223.3 KB)
and separated:
U-Box bottom.stl (137.1 KB)
U-Box Top.stl (86.3 KB)
An impromptu user-guide:
The design is intended to work with standard hardware that can be purchased locally. The slots in the side are for lock nuts; they measure very close to 6mmx9mm and are hexagonal at the end. You should try to get hardware that is as close to this size as possible so that the nut is unable to turn in the slot when you turn the screw.
I find it’s easiest when you insert the lock nuts “upside-down” so that the screw hits the side without nylon first. This helps get thing aligned to prevent cross-threading.
Use countersunk flat head screws to hold the enclosure closed. That’s what fits best.
I used standard #8-32 x 1.25" screws and lock nuts for mine. I guess metric is more universal but I went with what was readily available to me 
The slot for the heatsink accepts a 3" x 1/8" (51.4ish x 3.4ish mm) aluminum bar which is poorly cut to about 145mm. . It should fit snugly if your print comes out nice and clean but if it’s loose, the ESC will hold it in place once mounted.
The larger hole between the phase wire holes is for sensor wires etc.
The holes inside the bottom align with the holes in the U-BOX housing. I drilled all the way through my deck and inserted “tee nuts” which are also #8-32 thread pattern. When you insert the heatsink bar (and even if you opt not to) you’ll be able to drop screws through the UBOX, through the enclosure, and into or all the way through your deck.
P.S. I like to drill out the hardware holes in the print with a comparably sized drill bit (I used 5/32" or about 4mm?) to clean up the inside before inserting my hardware and to knock out any stringing/globs etc that might be an issue. It’s quick and ensures a clean fit.
The lid is not symmetrical so it will only go on one way (just to save you guys a couple hours of frustration since you spent so much time reading this post) 