Steve -
You don't need anything too expensive or complicated. Some of my friends use the veggie bags you get in a supermarket, or for slightly tougher ones - bread bags.
Use a wool sock liner first - my favorite are the SmartWool. Then the vapor barrier, then a good wool sock, and finally your boot. The barrier will cause your sock liner to become quite wet, but only up to a point. For reasons that aren't entirely clear (at least to me) most people's feet stop sweating after a certain point when using vapor liners. What IS important is that you put on dry socks socks in the evening - can't stress that enough. Otherwise, you run the risk of trench foot. If you're curious what that is - just Google it. Pictures of the condition are not for the faint of heart.
Of the Google search, this
one is probably the best. Try to find the simplest/thinnest ones. You want to avoid excess material bunching up in your boot. I have a basic pair that I got many years ago from a company which doesn't exist any longer.
But first, I'd try the veggie bags/bread bags. Vapor liners are a bit of an acquired taste. Not everyone likes them.
