I needed some boxes since, like many reloaders, I had a large number of lee and rcbs holders lying around that could stand to be better organized. I found one and it was nice, but I didn't like the holders sticking out of the top, nor did I want to waste precious filament on a tall shell holder for my lee priming holders. So using that project as inspiration I created a wide set of shell holder trays for Lee and RCBS holders, both 2x4 and 3x4, with lids.
Cad files are included. Poke about to your heart's content. This is my first ever model and I made it with FreeCAD, some calipers, an old Lee tray, and lots of holders. I do not know CAD best practices but I am reasonably certain my files are terrible. But I have printed the finished STLs, and they I can assure you are quite functional.