Reworked this in Blockscad3D:
(go to the editor, download the XML from: https://github.com/WillAdams/Design_Into_3D/blob/master/designinto3d_box_fitted_blockscad.xml import it, and experiment)
Or, use the Customizer in OpenSCAD: https://github.com/WillAdams/Design_Into_3D/blob/master/designinto3d_box_fitted_openscad.scad
I’ll probably get it posted to Thingiverse presently, then will start in on the vectors (starting with lualatex and METAPOST) and then try to work up a TPL (Tool Path Language) file which will cut it out automatically.
If anyone has any thoughts or feedback I’d be grateful.