I have updated the original customizer script to allow making tiny boxes. Now it is possible to make small generic containers with the original Customizable card box script.
Another update is the hole on the top. It makes gripping the cover easier, but if you don't like it, it can be disabled in the customizer.
Lastly I have added a size and plastic saving option called "thin bottom" which reduces the height of the model by 4 millimeters, without sacrificing practically anything.
Remember to add some softening material to the bottom if you intend on storing a cpu inside this container.