I too have kept a silica gel pack in the safe - and it has yet over two years to change color - IIRC the exposed bit will turn pink when it needs ''refreshed''.
I had been going to fit a small heater rod but have never bothered.
Thing is, despite high summer humidity - my office building has AC and so it never gets very humid inside - and in winter I have flued gas heaters so again - moisture levels modest. State of silica gel and guns in safe, and those longarms outside of it - show no degredation from any humidity.
I do keep blued guns wiped over with CLP or similar anyways.