How often should you use cleaner/conditioner on your roof?

Thanks for all the info, when I wash the roof, usually wet it down, have a bucket of hot water and a mild soap and a long handled soft brush, go over all the roof, front to back. Then take the Thedford Premium Rubber Roof cleaner/conditioner, spray in on, brush it in then rinse off then wash sides of camper. Just trying to keep my camper looking nice and last longer. I also realize the sun's UV rays are hard on things and that's why I keep it under roof all I can, but then its dust and birds.