Here are 2 examples of the Polygun bag:
http://www.polygunbag.com/gunbags.html
http://www.exploreproducts.com/kleen...storagebag.htm
Here are the Bore Stores which look more like the ones Soberbiker has:
http://www.borestores.com/
I've also heard of people using dessicants and airtight vacuum sealed bags.