I am building a surround for a large soaking tub. The wood is solid quartersawn white oak, and it is being built in a mission-style stile-and-rail design. The bathtub will be undermounted and the deck surface will be Silestone, with a 1.5" lip all around. I was originally planning to finish the surround in polyurethane, but several people I have spoken to tell me that polyurethane seals the wood from the air as well as water, and that I would be better off with a tung-oil finish (such as Minwax tung oil finish), either the oil itself or tung-oil varnish (such as Waterlox tung oil varnish, which I had applied to wood floors). I am concerned about water stains, although the potential for water will be occasional, not constant. Also, as it is a bathroom, the air will be somewhat humid after showers. I'm looking for guidance as to the potential for using tung oil rather than polyurethane. What are the pro's and con's, and am I asking for trouble if I use tung oil. I would rather not coat good white oak with poly if I can help it. Is tung oil adequate protection from the kind of moisture likely in a bathroom?