[Franco]

Hey Willy,
I'm guessing it is the thin stringer your talking about. Usuall it has a plywood core of 3/4 inch plywood wrapped in wroven - thats the heavy duty fiberglass cloth - it is used to support the deck. I would pull the gas tank to gain access to the stringer - easiest way to get to it and you could repair it from the side. Once you get the tank out I would drill some holes along the length of it to determine how much of it is wet. There are two schools of thought here - one is you can drill several 1/2 inch holes along the bottom egde to allow the moisture escape, one it has all drained use a heat gun to finish drying it out. You can seal the holes with some fiberglass cloth and drill several smaller holes along the top edge, and use something like git-rot. Thats a penetrating resin that is very thin - it could take several bottles to fill up that void.
Or once you get tha tank out you can take a grinder and cut open the side of the stringer and pull out the damaged wood core and splice in new plywood - you can bevel the edge so the to pieces over lap ( scarf joint) to add some strength. I'd rough up the inside surface of the fiberglass so the new stuff will have something to bite into. After you fit the pieces ( close is good) cut a piece of fiberglass cloth 6oz I thing about 8 inches longer the the plywood - wet the existing fiberglass and the new core with resin ( old paint brush works fine) lay the cloth on the new wood and wet it again with resin and put it in place - the cloth will fill gaps between the two pieces and add some strength. The hard part is clamping it together - You gotta have the clamping figured out first and dry fit everything prior to using resin. After it is all glassed on that side wet the exposed side, put on new roven - the heave stupp and over lap the edges. Call me if you want and we can talk, I know you got the number.