Hello Jean and welcome to the forum. I am sorry to say that the belly band leak is a common issue with Trilliums. We have a "new" one that had leak issues and so I have some experience with your situation. Prior to repairing ours I spent a lot of time reading about belly band
leaks on this forum. The short version is that when the two halves of the trailer are joined the belly band on the outside and a series of washers connected to the belly band by rivets on the inside hold things together until the halves are fiberglassed together (on the inside). Over the years water infiltrates though the rivet holes and causes the washers to rust. As they rust they expand causing breaks in the
fiberglass and
leaks. My suggestion is to use the search feature to see what others have done to deal with the issue. The search function allows for a google search, third option down as I recall. "Trillium bellyband" should give lots of good posts on the subject. Hopefully yours will be an easy fix. good luck, Raz