It have tested it with a normal 3x3 (as in the picture) and with a 4x4 and does its job without a problem.

Print Settings

It can be printed as it is.

Printed in PLA, without supports or rafts, at 0.2mm resolution and 15% infill.

Post-Printing

I would recommend putting some weight if you have heavy cubes just to give some more stability.

Also could be a good idea putting some adhesive clear rubber feet at the bottom.