I used 0707070s snap fit boxes for past projects. Sadly OpenSCAD isn't really what I'm usually using and editing STLs in FreeCAD is kind of buggy, so customizing them wasn't that much fun. To make my life somewhat easier I modeled a similar design as a customizable FreeCAD box.
Inside the FreeCAD file you'll find a spreadsheet named variables. Open it and change width, length and height according to your needs. The resulting model should update automatically. Keep in mind these are outer dimensions, so ff you're looking to fit something specific inside, take this into account. Wall thickness should be adjusted for your needs, 0.8 as used in the template is pretty thin and might not fit your needs when using PLA.
Tolerances are quite tight, opening or closing the box may require additional force and/or tools.