Not an expert on this matter but if it were mine I would open it up spray it down with a good awning cleaner with mildew cleaner and scented dish washing liquid on Both sides and scrub where I could get to with a hard bristled broom as best I could. Then rinse it out , let it air out on a good sunny day. Make sure it and everything else is totally dry before rolling it up. Then store under a cover and if that option is not available open after each rain on real sunny days even if it means moving the rv to a different spot in the yard to get the sun on it.