I've been searching for a decent desiccant system for my gun cabinet but while searching for one decided to make one in the meantime.
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
Drill multiple holes in the soap dish for better air flow. I got my soap dish from the dollar store so it was a really cheap flimsy version. There's better ones out there. Drilling holes too close together will cause cracks between the holes if you put too much pressure on the drill bit.
Step 2: Add Magnet for Simple Mounting in Gun Cabinet
Put the magnet at the bottom of the soap dish. This will make it simple to mount to any steel surface. This step may be skipped.
Step 3: Pack Desiccant
Pack all the desiccant that will fit in the soap dish. Packing it too tightly may make it more difficult for the packets in the middle of the pile to be effective.
I also wrapped 2 rubber bands around the soap dish to ensure it stays closed if installed upside down.
Step 4: Mount Desiccant Container
At this point the desiccant container is done. You may affix it to any metal surface, or simply put on a shelf. I added the magnet to this build to keep the container out of the way.
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".