A simple, small two piece case with 3mm hole mounting tabs for the little voltage meters you can find for variable power supplies. The model I have says DSN-DUM-368 on the the back. It is the one without the IC on the bottom, it has it tucked underneath the LED display. I am not sure if it will fit the models with the chips on the bottom but I will try it if I get any and see. I you try it and find out it works or not then let me know! There are (3) different cases. One with the gap for the wires on the right like the one pictured (that's the only one I have), one with the gap in the middle as I have seen online, and one without any gap in case your wires are somewhere else and you want to drill it out or have them run out the back.

Edit The case does not quite fit the meters with the chip on the back of the PCB. I will try to do a version for those style chips when I get some in.

Edit 01/02/18 I added a case to fit a meter I got in with the circuit components on the back with center oriented wires. The mounting holes were smaller than the other meter I had as well. I unit I received was marked V20D-3P-11 on the back and hopefully it fits similar units.