If you use a product like Damp-Rid, instead of buying their refills just go out and purchase some Ice Melt -- calcium chloride --- and use that instead. It is the same stuff and vastly cheaper. I will be doing a post on this next month. http://twodogsandasinglelife.blogspot.com
Yes. I have heard reports from gun owners warning against using calcium chloride desiccants in gun safes because those who have done so find it causes corrosion.
I personally find that neither calcium chloride nor silica gel nor charcoal (??) is sufficient to deal with the moisture issues I encounter vandwelling in western Washington's rainy, humid, cold climate. I have put all three to quite thorough testing (though the charcoal was solely for air purifying, the fact I was using a bunch of it and then attempting to tackle my moisture issue speaks for itself).
Desiccants typically absorb moisture at a slow rate, thus they work best in enclosed environments where the rate of new moisture introduced can be less than the rate at which they're drawing it from the air.