To mount the top, holes are designed for M3 threaded inserts. Screw holes in top are countersunk for M3 as well.
Outer dimensions are: 85 x 85 x 30 [mm]
Inner dimensions are: 80 x 80 x 25 [mm]
No supports needed when printed with closed surface on printbed.
Tolerances are tight but should snap together nicely.
The author hasn't provided the model origin yet.