Without knowing the history of your trailer, I would guess belly band or window leak. Ensolite tends to come loose from water leaking behind it.
Many "redos" I have seen were more cosmetic in nature. Endless threads on how to fix belly band and reseal Trillium windows
Perhaps prior owner kept trailer covered when not in use and did not see the leaks
Tradition caulk for windows
= bad. Butyl tape under window frames = good.