To insulate a mobile home addition with a low-pitched roof, consider using closed-cell spray foam insulation, which provides a moisture barrier and effective thermal insulation. Ensure proper ventilation in the roof cavity to prevent moisture buildup; ridge vents or soffit vents can help promote airflow. Additionally, use a vapor barrier on the warm side of the insulation to further reduce moisture penetration. Always monitor humidity levels and consider a dehumidifier if moisture issues persist.