Thanks! Glad you like the idea. (TL;DR at the end.) I just took the bottom panel off and, while there's plenty of room in there, I'm not seeing an immediately apparent mounting location for any sort of part. Once you've got yours fully wired up and working, I'll go ahead and pick up the necessary parts to get mine connected. This will give me an idea of wire lengths, etc. Once I've got that, I'll probably need to disassemble most of the shelf to get a better understanding of the possibilities.I love the idea of a 3D printed mount I have not peeked inside yet, so not sure what is needed. I certainly was planning on just zip tying inside the enclosure because the shelly is not weather proof, and the wire connection screws are somewhat out in the open.
After looking at it for only about 5 minutes, my quick assessment is that this will likely require a couple of holes to be drilled somewhere. The question is whether I can find a location that won't require everyone else to also disassemble the shelf. I'd like to make this as simple as possible, but proper placement may negate that desire. The shelf looks to be a sort of inverted "nested box" design with he black portion fitting up inside the stainless steel. They mounted the circuit board on the stainless steel and the nested design is the likely reason. The front of the shelf is bent, meaning it's solid, so there's ZERO chance of any liquid getting down there and making contact with the board. The display is most certainly sealed to the cutout with a gasket or actual sealant, which, again, means zero chance for liquid to get in there.
On the other hand, because the black metal insert is technically "upside-down" (big, flat surface facing down) when it gets inserted, that creates a non-sealed edge where the sides meet the stainless steel. As a result, this isn't where you'd want to mount any electronics. Now, due to the limited space at the front display, this may not be the best spot, either. Plus, any screws would be staring you in the face at the front and, I don't know about you, but that would irk my bit of OCD.
TL;DR: I've got some ideas, but I'll need to wait until I've got a relay wired up before going any further. I look forward to following along and getting this working.