Have to agree, camera bags are not airtight but I do think they provide an relatively controlled airspace and still worth a silica pack. Not really planning to use my bag as the actual storage unit. I have a timber cabinet with glass doors ( much like the camera shops) that I am setting up for general storage and the bag for outings etc.
Anyhow, I am working to supresee my paranoia :-), maybe it is not as scarey as my first impressions as long as you take some simple recautions.