Flat large enclosure for inserting Three (3) Breadboards, with 4 power Rails (see pic)(162x55mm breadboards).
Take two power rails off and assemble the three boards together.
Size of the box/enclosure recess : 162x144 mm.
Total size of the whole thing : 180x180 mm.
Add Two(2) Positive Banana type Female Terminals/Connectors,and corresponding negative.
Eventually (if you have the will...) route small wires soldered to the Power Rails of the fisrt breadboard to the Plus&Minus terminals.
Glue/Stick/doubled sided tape the breadboards to the recess in the enclosure.....

Use the STL and print at 0.25 mm height, that's sufficient, unless you wanna go crazy detailed !! My Speed = 70 mm/s, Ventilation 100% with PLA.

Have Fun