Okay, more research! But first let me say that this is a great forum because Bob asks a simple question and we all get to debate this in a civil manor (at least thus far!). So this is probably more than Bob, the OP, ever wanted to know but it’s something I always questioned myself: what do those goldenrods really do, if anything?
Joe, I found this article which explains how RH chemically contributes to corrosion/rust.
…the RH dependence of metal corrosion reactions is complicated by the inevitable presence of water soluble salts, which begin to absorb water from the air at a specific value of RH, above which they provide a film of watery liquid which vastly accelerates metal corrosion reactions.
From
http://www.padfield.org/tim/cfys/soroe/soroe.php
I do agree with you Joe in that corrosion may still occur in warm air with a lower RH, but corrosion is at it’s worse when the RH is high. If you look at the previous links you'll see that the RH is the first environmental priority.
So to prevent corrosion:
Most importantly: Coat the surface to prevent interaction with water
Secondly: Keep the RH low, below 50%
Lastly: Avoid high temperatures
Consistancy is good too, but I'm not sure the goldenrod really helps in that area.
I bought the Extech RH monitor yesterday at U-DO-IT Electronics (I got the last one). It works okay for the price. My safe reads 67% RH, at 72 F, which is a lot higher than I thought it would be. I’ve had the safe for about 6 months and thus far have not had visible corrosion problems. However I do keep my firearms very clean and most of them still have their original finish. The glock frames show absolutely no signs of corrosion
According to the Psychrometric chart (now how geeky is that!), if get a golden rod and it raises the temperature by 5 F, then my RH will be 58%. If it raises the temperature by 10F then the RH will be 49%.