I added my externabond to seams, fans and skylights when the camper was brand new and the roof was still clean. The dicor didn't have time to experience any deterioration from the sun and the externabond claims to last 12 years like the roof. My peace of mind is that I'm pretty bulletproof. There are always going to be exceptions but I tend to not worry about my roof which gives me extra time to worry about other things that might fail.
The roof should last a lot longer than 12 years, I was a roofing contractor and PVC and TPO roofs had a lifetime warranty
2003 Dodge Quad Cab 3500 SRW LB Cummins diesel, Banks Six Gun, Banks exhaust, Mag hytec deep trans pan, and Diff cover. Buckstop bumper, Aerotanks 55gal tank, airbags, stableloads Bigwig stabilizer, 2003 Lance 1071 camper, solar and generator