I use Blender for modelling, and really like this simple, yet versatile rugged box for many of my projects. As Blender operates on a mesh for imported STLs, redimensioning and moving features around is a bit more time consuming as I would need to observe face overlap and such to avoid manifold issues. In particular this is relevant when reducing the size of the box or moving the latches.
Using this model, it is all about just grabbing the vertices of for example walls, latch structures and moving these to where you want them and the mesh would still be manifold.

The author remixed this model.
Removed unnedeed vertices and faces to make it simple to further adjust by moving the different pasrt around.
Curves and details kept.