To repair a leaking motorhome roof, clean the roof, and coat the problem area with rubberized leak stopper. Apply the compound to the areas where you think the problem might arise later, such as seams. If the hole in the roof is too large, apply some roof repair tar to the area, place pieces of fiberglass screen onto the hole and cover it with tar again.
When cleaning the roof before the repair, wash it thoroughly while removing the remains of old repair materials and debris. Use a screwdriver or a flat scraper to remove the materials, but use the tools carefully, as you can punch through a thin roof. Allow the roof to dry completely before proceeding. Use a brush to remove water pools to speed up the process.
Wear protective clothing and gloves that you can easily throw away when you work with the rubberized leak stopper, as it is impossible to remove from fabrics. Similarly, use a disposable paint brush to apply the compound. Coat some extra leak stopper around the edges of the problem area to prevent the roof from leaking again. Spread the leak stopper thinly but widely, and coat the leaking areas and nearby seams thoroughly.