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Yeah, Keepit, if you're building the room from scratch, throw an exhaust fan in . Not just for the TV, but for the wood, windows and the general comfort leval in the room. Without ventilation, it would be like taking 5 or 10 showers in a small bathroom. The room will get quite damp.
You may wish to look into the new wallboard that is NOT fiber based. It's a bit more expensive but, not that much more. It is mold/mildew/rot resistant. It has no paper backing on it at all. A best buy for moist areas.