Not so difficult to design in Solidworks or OpenSCAD, but just so you know 3D printing resolution for the plastics you really want nylon/ABS are limited and making a cover which snaps on vs one held with screws can be tricky and will almost surely require some post processing with acetone and some grinding; even then the strength will not be even 1/3 of an injection molded part.
If you could make technical drawings with all of the minkowski circle to rectangle combinations angles etc for the edges and where the snap lugs are I could throw you a prototype if you have access to a 3d printer. I need measurements accurate down to at least 1/10th of a mm. You can hand draw pretty badly and photograph just so I get an idea, the only important thing is the measurements and angles are correct. In fact you can post them here and if I do not check this thread for a while PM me.