After you brace the sides of the hull and remove the old deck, check the
stringers and transom for rot. Be ruthless, remove all affected wood, else all
your work will be wasted since the damage will continue. Remove all
questionable foam. Even foam advertised not to absorb water will to some
extent and hold it against the wood. ALSO! If the gas tank is aluminum remove
it and check the bottom carefully for pinhole corrosion etc. Typically the
alloy tanks are foamed in place which sets the stage for trapped moisture
corrosion. Any doubts at all, replace it with a plastic composite tank. A fire
on a boat is ugly as it moves faster than you can imagine AND there's no place
to run. Tab in the new "wood" carefully to match the orig. structure, leave no
area open to new moisture penitration and allow for ventilation if at all
possible!
As you have guessed, I have been down this road before.
Best wishes
Mike