My Stumpjumper had cloth tape wrapped around the chain stay to prevent chainslap. The rust from the moisture it held I'm certain is far worse that any damage the chainslap could have done. If you're really worried about it, I'd give Teflon pipe tape a try. I can't say that it would work as I've never actually tried it. It does seem like a decent idea, reducing some of the friction if rubbing occurs and wouldn't hold moisture like cloth.