Supported by the tub, the inside edge has taken some hits. Over the years, this damage has progressed to the point that it has become a thorn in my backside. . I'll be using epoxy. That I can see, there's no alternative but to grind down into the edge of the tub, and build up several layers of fiberglass--use cloth? Seeing that this area is likely to be damaged again, how large an area should be ground down?