It reuses 4 of the m3 screws on the standoffs. They screw directly in the hole in the bottom of the box. 

Doesn't need supports if your printer is good with bridges. Maybe little supports for the conterbored holes on the cover.

Need 2x M3x6mm/8mm to hold in cover.

Can be directly monted to rig with M6 screws and T-Nut.

I made the tab holding the cover bigger since I found it a bit flimsy on mine. Ddn't bother to print it again.

Can be printed in any material, I used red Polymake ABS.