After talking to a few friends that rebuild surfboards I took their advice and applied Hysol to the interior area where it was likely that I would sand thru while reshaping the wingtip. Once the Hysol was dry I sanded until I got everything where I was happy with it. Some of the areas did go all the way thru and into the Hysol. As they suggested I then reinforced the sanded areas with fiberglaas from the back side. I'll see how it worked tommorrow when it is all dry.
