Hey, nice of you to do this, and I’m sorry to rain on your parade… 
But your model has a few errors, I’m not sure it can be printed as it is. The top plate does not touch the vertical walls on 3 sides, there’s a 0.004" (0.1mm) gap. The small tab on the short side hangs in the air as well.
Apart from DWG and DXF (and STL of course) AutoCAD can only export to ACIS (*.sat) which is a proprietary format that cannot be opened by open source software. Expensive CAD software usually provide translators. There are no 3D file format that AutoCAD can export to that could be opened by open source software. STEP is good because it’s an open CAD exchange format, but of course AutoCAD does not offer it. Autodesk Inventor does though. Go figure.
As for scad, it’s the OpenSCAD file format, and the only CAD app that can open OpenSCAD files is FreeCAD, an open source parametric CAD software. Although OpenSCAD needs to be installed too (I wrote about it here). OpenSCAD is a niche program for programmers, AFAIK virtually no one outside the RepRap/Personal 3D printing world uses it. That people use it at all baffles me to no end.