In the hymnal 3″ tape is applied to this edge on page 257, where as the bottom and transom are fiberglassed earlier on page 192.
I suggest applying the tape much earlier, immediately after installing the transom page 188). Then later when preparing to fiberglass the bottom (page 192) fair the bottom edge of that tape on the transom (I used a grinder (carefully and with respiratory protection but a dust extracting RA sander would work as long as you stayed off the softer okoume). Then leave a 1″ skirt dangling over the transom when cutting your bottom/transom fiberglass swaths. Don’tcut or file away this skirt until after you have filled the bottom/transom cloth weave (epoxy fill coats) as it will absorb all the inevitable epoxy drips and keep them from getting on the gutter. Once the fill coats have cured, take a coarse metal file and file away the skirt, fairing it into the 3″ tape you installed earlier (page 188) rather than later (page 257).