Just run the fan longer after the shower. Unless you saw evidence of mold or mildew while taking off wallpaper, etc, running the fan longer will do quite a bit of good. We generally run it five to ten minutes longer after we are done with the shower, and this is a 100% enclosed, small, no window bathroom. You might also want to check the exhaust fan ducts to make sure they are not clogged. Dryer vents aren't the only vents that can clog!