I have seen underfloor heating in a few but, of course, switched outside the room.
One of banks used to have a simple electric flex running in to the SR through the door. At night, last thing before closing, the manager simply unplugged it and it swung inside. Of course inevitably he sometimes forgot and plenty of them were cut and repaired.
I have used a dehumidifier in a strongroom that had to go into use asap after construction. I think that was a shame as a slow cure would probably have made for a better structure. That one had mains inside, although switched from the outside, so the dehumidifier could be left running overnight. There was no day gate so I suppose the SR must have been kept closed and locked almost all day.
