I was up on the roof of my 2013 Arctic Fox 27 – 5L fifth wheel last week and I didn't see any caulking that Was in the condition yours is, and I haven't touched up the caulking since I bought the Arctic Fox new.
I'm a full timer so my fifth wheel has never been indoors because I live in it, so I get up on the roof and check things out fairly often and I haven't seen a need to repair any of the caulking.
Just guessing here, is it possible when the trailer was new before you bought it, there had been some kind of accident and the insurance had it repaired improperly? Just a thought.
theboondork.com