Based on PatrickT's design:
-OpenSCAD files provided, which import the original stl files, and allow you to turn modifications on/off
-Made it 2% larger because that's what my printer needed to properly fit my Pi.
-Option to add pads at the corners, to use with double sided tape or screws.
-Option to add gnubs, which fit into the Pi's existing holes, for a stronger fit.
-Option to make a shorter version, which uses slightly less plastic, but doesn't completely surround the Pi.
-Option to add arches to reduce width in the mid-section, useful when fitting in a smaller box