My mother used to put rice in our salt shakers all the time to keep moisture out of the shakers. But you can buy regular desiccant to put into your safe to solve that situation. They sell a lot of items with the little desiccant bags: for instance my micrometer came with a dessicant bag in it. Try an old cotton sock and put some rice in it and see how it works. It sure won't hurt anything. And don't use instant salt- go buy a 1lbs. bag of regular salt in the plastic bag. That is what she used.
I have DampRid, sock full of rice, arm and hammer baking soda all in the safe. The new rifle gun cabinet has two packets of Stack On silicon crystals. All the long guns have also been Ren waxed. Will keep an eye on everything for any problems. I actually noticed some rust on my shotgun barrel and I got to thinking that was same spot where the rice sock was against the barrel.
After reading up on DampRid and finding it is made of calcium chloride which is actually a metal corrosive and is not advised for places with metal objects due to causing rust. HMMM.
If you want to make your own damprid products then check this link out. Much cheaper than buying damprid products.http://www.thriftyfun.com/tf66086483.tip.html
Do you want to know how to make your silica desiccant packages then check this out. Super cheap to make. This is what I am going to try.
Here is another DIY method.