More than likely it is. After spending some time around Tin Can Tourists, it seems like all the old trailers (older than yours) suffer from leaks from around the roof vents or windows. That's usually where they have the most damage at.
Now whether it's the butyl tape or the actual seals on the window, that's a hard call. Probably some of both...
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR