Dessicants need to be recharged (dryed) unless they are in a completely sealed environment. I worked with vacuum sealed chambers and molecular sieves (dessicants) They degrade, even in an absolute vacuum. So, your safe isn't sealed or a vacuum. Dessicants will degrade, and rapidly if they are in high humidity. How can you tell? A hygrometer? A hygrometer won't tell you your dessicant is saturated accurately. Add those up and your labor. Goldenrods are now cheap, by comparison ($16.99). Mine is over 10 years old. I check it once in a while. It works. No rust. 7 watts. Get some!!!
A 5-10 watt light bulb will do the same thing!!
I live in the desert. Often, desert folks run swamp coolers. My house is at 55% humidity right now, with it being less than 20% outdoors. Even if you run AC or heat, often folks run a humidifier to prevent dry skin/eyes/balls/nose/etc.
Midway linky