There are several pre-generated variants with reasonable parameters you can just use.

Or you can use the OpenSCAD source to generate your own variant by simply altering the parameters.

The important parameters: number of slots for lab tubes (1 or more), size of one slot, compactness of arrangements, extra spacing between slots and height.

Width and depth would then be implied by those settings.

Note that with too little slots there may be lower stability and with many slots (more than 15) you may need to increase wall thickness in advanced parameters to ensure durability.

No supports, no complex assembly - just print and snap the two parts together. Small assymetry in latches will prevent snapping the two parts if you do it with incorrect orientation.