Liquid Roof is a specially formulated version of Liquid Rubber that has the flexibility needed for vehicles that are traveling and causing significant amounts of tension as it travels and turns. If your RV is stationary the entire year you can order the Liquid Rubber but if you do travel with your RV you will need to purchase the Liquid Roof. Note applying the Liquid Rubber over an RV will void its warranty. Source: https://www.epdmcoatings.com/mobile/liquid-roof.php