Humidity in the safe generally ranges from 51% to 55%, which from what I understand is just about what gun museums shoot for.
Remember though, that temperature is part of the equation. IIRC, the NRA advises museums to maintain 50% humidity @ 70°F. My basement stays in the low 60's, so that translates to a slightly different dew point temperature.
Now that Griblik is well below 50%, I'd say his plans, to turn off the heater and seal up the safe for a bit, are right on. That safe is pretty much dry as a bone now, or will be soon
(no telling how much moisture was in that lining). The humidity will surely rise after the heater is out, and make sure to empty the Dry-Z so that the water in there doesn't just evaporate and
re-humidify the safe. If/when you see the humidity rise back up above 40%, don't fret, you'll need it to be up there anyway. As mountainpharm mentioned, too low humidity can cause changes or damage to any wood furniture on those guns.
It looks like you've licked it!!
My regards on the Kimber.