I keep 10 bags in my large safe, and just to be safe, I dry 5 of them every six months. My safe is located in a HVAC room, too.
When I go shooting or hunting, I place one bag in the gun case, and dry it after returning.
The reason I try to send 10 is that a USPS flat rate box will hold that many with no shifting. I seal them in a plastic bag inside the box.