At Hermit Creek and Boucher Creek two weeks ago I hung an ordinary stuff sack with my food in it, no problems. My friend had a Ratsack. They couldn't get into it, but anywhere that the plastic bags inside came into contact with the mesh, as Te-wa said, they nibbled a little bit, tried to pull the plastic through. But, then again, my friend didn't hang the Rat Sack. http://www.armoredoutdoorgear.com/
There are racks at Hermit Creek for hanging up all your gear, including your backpack.
You can buy Rat Sacks at Peace Surplus in Flag.
Another thing to watch out for are the ravens. If you leave water bags lying around they will sometimes peck holes in them. I especially have had this problem if there is no good water source nearby. I learned to hide water bags under rocks. Have had no problems since with ravens.