The RPi should at the end stay in the main cabinet with all the wires and the PLC. I have built a DIN-type case. It is not an ideal project but allows to bring some order to the whole thing.
At the end it all is very simple. I bought a Z108 Kradex case, used a sharp knife, some files, the GPIO replicator described in an earlier article ...and some patience:
I used some wall plugs to mount the RPi to the case. It is not perfect... one should use plastic pins and a decent glue...
After the RPi and the replicator got mounted and the needed wholes were cut out, the whole thing looks as follows (on the left):