This is the OpenSCAD code for small, thin walled parametric box. The basic idea is that all the sides are 2-extrusion thick. The chamfer on the top and bottom forms a clean base that is easily removed and the filleted corners seem to add some rigidity. The chamfers are all hard coded at 45 deg to allow easy support-free printing.

The code generates three basic parts: end caps, the main body and coupling sections. To make the base, I combine an endcap with walls and the coupler. The cover is simply an endcap with a copy of the main body, but with the height adjusted. The 'position' parameters sets the ratio of the base to cover height from the overall height. The cover is rendered next to the base as a single STL model.

Be careful if you make changes in the 'Expert Setting' section. Some combinations of the fillet radius and chamfer size can cause the inner wall radius to become negative, usually resulting in a solid endcap. Also, no check is made to ensure the coupler section will fit inside the cover. The tolerance of .15mm seemed to work well for my printer but the fit will also be effected somewhat by the coupler size and the overall box dimensions. Somewhere between .1mm and .2mm should be fine. Finally, a large number of facets may make for smooth corners but can can also make the model needlessly complex and slow down the customizer. The facit value is multiplied by 4 when applied to the $fn internal parameter, so value of 5 here generates a 20 sided cylinder and for and for a 3mm radius this seems like plenty.

The code includes a boolean to select whether or not to generate the lid, but I'm not sure the Thigiverse customizer supports this. If not and you want an open box, set the height and position so the lid give you the desired size and split the model with your slicer. Or you could download the code and run it on your PC.

Note: the Thingiverse customizer works, but it is very slow. I recommend downloading the script and open it with OpenSCAD. Then can edit the parameters or use the optimizer locally (go to window drop down and uncheck 'Hide Optimizer')

The Cover Photo shows a box I made this morning. The first screenshot shows an example of a tall skinny box with the native OpenSCAD customizer. The second shows a cutaway view so you can see how the chamfers are formed.

Enjoy! Bob M