Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2498123.
I use electrical outlet junction boxes quite often as project cases when dealing with AC. It's easy to find low profile single gang boxes, but not so much triple gang boxes. I whipped this up tonight in SketchUp (yes, people do successfully use SketchUp for 3d print modeling) after a trip to my local hardware store left me empty handed. I only needed the 3-gang version, but the other two were easy enough to extract so...
For my particular need, I only needed mounting holes in the bottom of the box and I needed one particular hole for the AC in line. This is a simple enough design. Using the CAD program of your choice, you can add mounting tabs or holes to suit your needs. Or, if you go with 100% infill, just drill holes as needed.