Classic Accessories 104151001 RV PolyPRO 3 Class B Cover - 20-23 Ft. Triple ply polypro 3 keeps out rain and snow. Thick&#44; triple-ply top and single-ply sides protect An integrated air vent system combined with quick drying polypro 1 sides reduce wind stress and vent Adjustable front and rear tension panels and elasticized hem corners provide a custom fit Integrated rope attachment system and a provided toss bag helps reduce crawling under the RV Zippered panels allow access to the RV doors and engine areas