Every time I unbox a new product I save the desiccant packets in a sealed container for use later. Here's how I reused the packets.
Hard Drive Magnet
This build was too easy. The titles of the steps themselves could have been enough of an instruction. I struggled to add fluff text to the steps to make an already simple step more understandable.
Step 1: Drill Holes in Soap Dish
Step 2: Add Magnet for Simple Mounting in Gun Cabinet
Step 3: Pack Desiccant
I also wrapped 2 rubber bands around the soap dish to ensure it stays closed if installed upside down.
Step 4: Mount Desiccant Container
Soap Dish - $0.75 (you might find this cheaper)
Hard Drive Magnet - Free (harvested off old computer)
Desiccant - Free (harvested off shipped packaging)
Rubber Bands - Free (harvested off Broccoli bunches or mail)
There's ways to re-dry desiccant packets, but I think the amount of time in the oven is cost prohibitive (cost of fuel or electricity for 2 hrs of drying time). It might be better just to replace the packets from time to time.
I don't think this will last in the gun cabinet for long. It is simply a stop gap measure. It gets pretty humid where I live and I wouldn't want rust to take its toll on my "collection".