Lou,
Where I live, humidy is high, dew points in summer run in the 60-70's. It's ugly when in the 70's. What happens in a gun safe is no different than what happens in a home. You don't control the humidity, everything inside will get moldy.
I have a tenant who insisted on leaving the back door open, which allowed 60-70 degree dewpoint air to come in contact with the 55 degree concrete floor and walls. Now the carpet in basement needs to be pitched. If bleach doesn't remove the mold, I have ordered a chemical that will, not cheap.
Controlling humidity in gun safe applies to everything. Guns rust, tools rust, welding rods soak up moisture, condensation collects on metal roofs, condensation forms on concrete floors in basements, garages, moisture in air compressors, moisture collects in gas tanks, even seen engine rust internally, freeze up. Fighting humidity is an endless battle in Indiana.
Some people use the moisture beads you talk about, which I've purchased at menards. I use 2 dehumidifiers in two different basements to fight moisture. One runs all the time, the other is for when the one can't do it all. I've heard of some welders using old refrigs and putting a light bulb inside. Increasing temp, lowers humidity.
I can only think of about 3 ways to battle humidity, one you mentioned using chemicals to soak up moisture. The other cool the air, AC or dehumidify, to make the moisture condensate out.
Third way is to warm the air, warm the inside of buildings, warm up the tools, guns. Heat lowers relative humidity, but more importantly if you keep the temp of items above dew point, condensation can't form causing gun and tools to rust. I think wd40 was invented to displace water keep guns from rusting in WW2. I have to keep my tools, lathe, drill press, saws, vice covered in oil.
I designed my pole barn with vented eves, a ridge vent, and a power vent. I put conventional vents in roofs, but also use power vents. Power vents lowers attic temps, it saves shingles by drying things out, and it saves on AC bill. You can always tell when attics are too damp, shingles will curle up on edges, shingles will grow a black mold, it shortens their life.
Good luck fighting mother nature, she has the upper hand.
George