Google. Belly band on Trilliums is a well known defect and removing the band, grinding out all the plates, and patching the fiberglass is the time tested repair.
Love my Trillium
but they had some serious design flaws that have to be repaired: belly bands, rotten wood around windows
, rotten wood where door hinges attach, and body to frame bolts. Pre 1976 had a recall for their frames. Front body bolts went right through frame at the same place frame was mechanically bent. Frames cracked.
First thing I look at when I see pictures of a used belly band. If it still has the old trim, I know I will be grinding and patching.