Bear grease is an excellent waterproofer. I doubt that it's as good of a moisture vapor barrier as modern finishes, but it will definitely keep water out of things. I used to use it to waterproof my leather boots, and it worked great for that. A friend of mine was rendering some bear grease out on his deck when he accidentally spilled it. He said that rain water beaded up on that spot for a year or more. With the grease finishes, it's more of a continuous process-regular greasings, warmed and rubbed into the wood.