Thanks my friend, your comment is really appreciated.
Openscad is not so hard to learn, it's relatively easy to build what you want
when you know each pieces allowed to you, like a LEGO.
About exporting to STL file, in fact, it's mostly made for that,
check the note, I added an animated demonstration of using the customizer
to export your customized box, piece by piece.
I hope that will help you.