The last person I'd trust to tell me my roof needs expensive work done immediately would be an RV shop, one of the guy's here got roped into a $12.000 re-roof job on the same issue! As I understand it our EPDM roofs are made to last at least the life of the trailer and it'll be the joints that will fail opposed to the rubber roof. Those dark spots you see are mildew and dirt and if the rubber looks "chalky" it's basically oxidation and nothing to get worked up about , twice a year I wash my roof with Dawn dishwashing liquid(non petroleum)inspect my roof and it's joints and treat it with Protect All Rubber Roof Treatment, that's all you need.
Now go have a cold beer and find some light, nimble young person(I use honorable grandson #2, he can bounce better than I can) to climb up on top of your rig to clean and treat your hard working rubber roof