Desiccants work best in a closed container, like electronic parts that are sealed with a pack of desiccant to take up and hold any moisture sealed in the bag. I don't think any gun safes are air tight, so air is continually being exchanged, especially when you open the door. Desiccants work on continually decreasing efficiency until they are dried out again. Forget to dry them out and you have no humidity protection.
I live in a very humid climate, and have never used anything but a GoldenRod. The idea is to keep the temperature in the safe two or three degrees warmer than the air outside the safe. Where humidity becomes a problem is when a safe in not kept in a heated and cooled area. If the guns cool off and then the air around them warms up, moisture condenses on the colder guns, and no amount of desiccant will prevent this.