Marc,

I replaced 16sqft of the deck core (22sqft total) of my S2-7.9.

I did it all lots of ways, but the one that worked best was vacuum
bagging. Not quite accurate in this description, but close enough. If
you can close of the rest of the core enough to get a good "suck" and
can get a hold of a suitable pump. You will have a better finished job
faster.

The inner deck does not have to be as heavy as it was laid in the
factory, because you get get the glass there with a lot less resin.
Three layers of 9oz cloth will do fine. Do remember that the last layer
has to overlap the existing glass by 1-1.5", and the others maybe 3/8
less.

As a vacuum job, you wet out the layers of glass, wet the surfaces of
the core and existing glass. Maybe put a coat of epoxy filled with
microlight or fillet blend on the surface that will go against the
inside of the upper deck to make it bed flat. You do all of this on
top of a board that has already got the sealing film, bleed layer and
peel-ply on it. You can even have the duck tape at in place if you are
very careful. With the pump running, slather it together and slam it
up there. You have to be sure how you are going to hold it until you
get it sealed off, but a friend's hand or a pre-cut stick will work.

Get the Gougeon brother's book on vacuum bagging and start there.

Matt Colie A.Sloop "Bonne Ide'e" S2-7.9 #1