My kids have a 24 pack of tempura paint sticks. The box they come in is pretty awful for repeated use. What good is a 3D printer if you can't print a box?
These have enough room for 24 (tempura.stl) or 12 (tempura_3x4) markers to be aligned in a zig zag. There is enough room to get the middle ones easily.
These are an example of the markers:
https://www.amazon.com/Pencil-Grip-TPG-604-Tempera-Paint/dp/B07SG15QMC
The author marked this model as their own original creation.