I am replacing my bathroom drop ceiling panels with lightweight 1/4" sanded plywood (not exterior grade) that I am cutting myself. I am planning on staining them and then putting on some kind of polyurethane or sealer. Does anyone have specific recommendations for what I should use to ensure moisture doesn't affect them..especially above the shower? The bathroom is small, poor ventilation, although I do have a small fan in there near the ceiling and leave the curtain open after showering. I do have cans of Helmsman spar urethane clear semi-gloss, Parks Gloss Polyurethane and a satin Minwax Polyshades. Perhaps one of these would work? Always nice to use up the stuff sitting in the basement. Thanks so much in advance for your suggestions.