I would have no connection except the obvious that the enclosure would be connected to 'protection ground'
Kai:
But then the enclosure cannot act as a shield! You will not have any RF shielding!
Better is to have a connection at least for RF, by the help of a cap.

With the enclosure connected to 'protection ground' the only RF you get in is the noise on the protection ground plus a wee bit from the enclosure to protection ground wire impedance.

If you put a cap between the enclosure and the signal ground, there is an effecrive RF short between the enclosure and signal ground.

With the inductor you get RF isolations, with the capacitor you get LF isolation, why not isolate aginst both with nothing.

I noted you referred to 'hum' I worry much more about spikes.

Erik