Roger Long wrote:

Can anyone point me to some good on-line info on plugging old through
hull holes in a fiberglass hull?

Any other advice appreciated. The yard wants 6% of what I paid for
the boat just to plug one and put a new backing block in another. I
hate working with glass but it looks like I'll be doing this myself.

Did you look at the Don Casey book about fiberglass repair? He has a lot of
good how to info and probably describes repairing fiberglass holes.
--
Bill Boyher