To eliminate musty odors in a crawl space, first identify and address the sources of the moisture, such as drainage or leaks. Improve ventilation or add a dehumidifier to control humidity. Clean the area thoroughly, removing any mildew, mold, or other debris. Incorporate a vapor barrier to prevent the infiltration of moisture and consider encapsulation for long-term odor control. In addition, consider using baking soda or activated charcoal to enhance air quality and increase the absorption of lingering odors.