You will need one or two rubber bands. Population Cubes should not fall though holes unless you pressed the device on both sides.
In case you want to modify it, I attached a FreeCAD project as well
In case you want to store it in the original box I also added model with cut corner (use it with one rubber band).
Practical advice:
I printed the bottom part in vertical position so I didn't need to remove supports from the furrows, but I advise you to experiment. There were a lot of supports to remove and I needed to use a file to flatten surfaces on holes.
The square part sticking out on the bottom is for better targeting.
The author marked this model as their own original creation.