I've had good luck stuffing crinkled up newspaper into the stinky cases and letting them sit for a while. If the outside also smells, you could stuff it, then set it in a bag full of newspaper for a week or two. Change out the paper occasionally. I do this when my big outside garbage can gets smelly, and it helps there, too.
For what it's worth, I keep my FW in a small roller bag. Never use the case at all!