We don’t recommend chemical erosion. Too easy to ruin the whole thing. Inexperienced builders may have a bad day. What we do is to use a 1/4 inch drill bit and kind of dig the foam away with the spinning drill. This is done at the same point you did, just before the nose blocks are installed. Use lead powder from a golf shop. Mix it with epoxy and pour in. Easy, and quick. Love the video!