I wouldn't use Fray Check. What I would do instead is fuse strips of Misty Fuse over the weak areas. (A nylon tricot fusible, such as the strips sold for joining batting pieces, would probably work fine too.) If you use Misty Fuse, just be careful to make this your last step before layering; otherwise, if you forget and iron after you have added the Misty Fuse, you could end up with fusible on your iron or have your quilt top stuck to your ironing board!