Well Snowninja, arfmel, and Enigma, after considering your comments I believe I've come across a solution that will not only solve my problem, but could benefit a lot of folks with large safes.
Silica gel is very probably the most available and cost effective desiccant for general storage of large pieces of metal stocked with wood in a pretty tight steel box which will be opened periodically.
Snowninja's concern hit home. I think we've all seen instances where a "safely stored" piece was damaged. I fondly remember the first reasonably priced stainless steel firearms coming on the market, so that dates me. But I think I have a solution...and this is in no way an endorsement of one product over another and I am not receiving any sort of compensation. In fact, I haven't done this myself yet.
Nalgene(TM) makes 1 oz. (30 ml) wide mouth bottles out of polypropylene copolymer (PPOC). This stuff is "autoclavable" and rated to 135º C / 275º F. You can get these for less than $2.75 each. I'm gonna use a small brad heated red hot to poke plenty of holes in the bottle and then fill it with silica gel. The small brad (nail) will be smaller than the silica gel bead.
I think this solves Snowninja's astute concerns about saturated silica gel packets contacting the objects they are supposed to protect and causing them damage.
IF (and that's a big IF) PPOC will routinely stand up to 250º, which is the usual temperature for regenerating silica gel, I think this will work for me and maybe y'all. Looks like you can get a quart size bottle for ~$13 bucks if you want to use it for your larger volume area. I'm gonna use a separate oven thermometer instead of relying on the dial. Those can be waaaay off. If you have a source of silica gel I think you're set. In a worst case scenario you can regenerate the gel in an oven, put it in an air tight vessel to cool, then transfer it to your ventilated container, Obviously you're gonna have to spend a bit more time with a brad, vise-grip pliers, and a propane torch for a bigger container.*
*WARNING: don't do this unless you are thoroughly trained and familiar with fire, hot pointy objects, and dealing with molten plastic. Do not do this near small children. Not only could they be harmed, but they may use this knowledge to bad affect later when unsupervised. And don't do this on the kitchen table if you are in a relationship.
I think this will work for me. I hope it does the same for y'all.