We purchased an older fifth wheel to use as a sleep camp. There is this musty/bad smell that is more prominent when I open the cabinet door under the bathroom sink as well as the cupboard under the k...
There are vents under the sinks that screw on to the top of a plastic vent line for the drain. If it has been sitting a long time these can dry out inside where the rubber valve is....try running the water to loosen this flap. you may have to unscrew tthem and replace. You can find them at Lowes, Home depot, Menards or most hardware stores.