As with many, my empennage fairing has fit issues. I began by cutting it in half along the spline. This helped me reposition things, then make more trims. Once things were close to correct, I began laying fiberglass cloth below and on top of the existing parts to fuse them together again. Several iterations of this provided a better fitting piece. I still need to do some final trimming and lots of finish work, but it should be a nice improvement.