I use them. I don't know how much they help but I am sure that they can't hurt. Also use them in my gun safes.
Yes, they are a MUST ! If you want to preserve your coins. But they must be used correctly. They do not last forever so they either have to be changed out as needed or re-charged as needed.
I also read where someone includes a roll of bright new pennies to act as an anode rod. Good or bad I don't know but the dessicant is a must! http://www.theruststore.com/Silica-Gel-FAQ-W40C2.aspx
This doesn't help on the moisture damage, but it would help in removing reactive contaminants from the air such as sulfur compounds. Also you didn't mention if your collection was coins alone or if paper (money,stamps,documents) were in the safe. Paper requires some humidity or it dries and fragments or discolors. Jim
I use these: http://www.wizardcoinsupply.com/product/silica-gel-unit-450-grams.html It's just silica gel beads in a bag, that is inside a box. There's a card meter on the box that changes from blue to pink as the bag gets saturated. This one is supposed to keep 33 Cu. Ft. dry which is quite strong for a small area. When you need to recharge it, you just take the bag out and cook it in an oven at 245 degrees for a few hours. They work great. Also use a dry rod humidifier that plugs in.
I use it, as well as new silver. Every few years it gives me an excuse to buy some generic white silver and throw in there loose. I like using silver since if I see it staying white I know my coins are being protected, but if I see it toning I know something wrong is happening.
I have both coins and paper currency displayed together and humidity control is even more important to organic paper. For what it costs, there isn't a better buy to keep your collections safe. Kind of a no brainer.
