Good report, Bob
I would only add one data point. You saidThere must always be
concern about an underlying
(but now covered) crack propagating into the laminate.

I have ground out literally hundreds of cracks in gel-coat that went right down
to the fiberglass laminate. To date, I haven't seen any gel-coat cracks that
entered the underlying structure. Not saying it can't happen, just haven't seen
it in going on 30 years of smelling fiberglass dust. BTW, I'm talking about
pure gel-coat cracks, not surface cracks that were caused by laminate failure
underneath. That is the first question that a repairman asks, Is this a
gel-coat crack or has the underlying structure moved?
JJ Sinclair