George,

You probably already know this but I will say it anyway for benefit of
others.  The ramps you added above and behind the top cowl openings quickly
and abruptly ended without proper tapering about 6 inches behind the
opening.  This created a very stiff section which abruptly ended at that
edge hence any bending forces were all concentrated at that edge. The thin
glass cowling could not resist that load and cracked. What was created was a
6 inch moment arm with a stiff rigid lever.  The solution is to taper the
reinforcement (like the fishing rod concept) to allow rigidity but
increasing flexibility to absorb vibration and stresses in a smooth
transitional manner without concentrating forces at a single point.
Eventually near the edge  perhaps midway or halfway back from the front the
tapering can be down to one bid of glass.  Think rigidity with increasing
flexibility and perhaps we may be able to solve the problem of stress
cracks.

Bob Smiley