A quick remix of the original, adding 2 small tabs for M3 screws.
This is for a single relay
5V relay on Amazon
As always, I've included the sketchup files.
I basically imported the orginal STLs, and just added the screw tabs and re-exported it to STL.
I've added v2 that makes the M3 mounting base thicker and hopefully addresses issues with certain slicer applications, I've used Cura with great success printing this case.
I printed mine with supports, just in the gap where the relay pins stick out, just for cleaner lines. You may not need supports