Our lake home has natural redwood paneling in most rooms, including in hallways below grade. In the summer months the redwood will mildew (turn black) and smell. I have used deck cleaner several times to wash the walls as best I can. (Also, there is a dehumdifier running where possible but it does not reach to the hallways). Is there anything I can do to prevent moisture rention in the walls that is safe for interior walls, ie. water sealer or should I poly some of the walls?