Small screwdriver; get a GoldenRod with the removable plug so only the bare wire has to go through the hole; caulk (I used fireplace mortar my neighbor had); and forget the dessicant.
Make sure the rod goes on the floor. I pulled the shelves out from the back wall about a quarter inch to improve air flow. Heck, I have 2 GRs in the safe. If you could see my gritty, unheated, damp 1916 basement you'd understand.
The GR works by circulating air through the safe and keeping the guns warmer than the outside air entering. No condensation, no rust. It doesn't lower the humidity in the safe much at all, it just keeps it from collecting on the guns.
I tried using a big box of crystals from the gun store and a huge tub of flower-drying crystals from hobby shop at the same time - it was a total waste, they filled up in three days or so. I tossed them years ago and the guns are fine sitting in the safe in my very damp basement.
John