If it's not leaking I would not put any coating on it myself. Most RV rubber roofs are made by Dicor; here is a link to their website with instructions for maintenance. Beware of any cleaning products that contain petroleum solvents per their website:
CAUTION: DO NOT use cleaners or conditioners containing petroleum solvents, harsh abrasives, or citric-based cleaners. You may cause irreparable damage to your roof and/or may void your warranty.
After cleaning, I treat mine with 303 Aerospace for protection.