What is inside the hull to back that stout stainless on the outside?

While in La Paz in 2004 I had a boat builder and a mechanical engineer design a new anchor system for Mirador that is very similar to your picture. You can read about it at http://www.svmirador.net/February_16_2004.htm.

Our primary concern was to ensure the strength of the hull and backing plate inside the hull. The hull at the bow was already 2" thick solid glass and we added another inch of glass. We then put a 1/4" stainless backing plate inside the hull.

Bringing the anchor load to the bow at the waterline has greatly reduced the movement of Mirador while anchored in choppy conditions and has reduced the tendency to shear side to side.