I recently I had to replace the stringers in my Scarab. Half of my stringers all the way up to the cabin were completely hollow. The wood had turned to dust in some places. I had to pull the entire boat apart to do this repair. Thank god i did some research on the web and OSO and I able to find a product called Sea Cast.
This is a parable transom and stringer repair. It is a polyester filler mixed with fiber glass that is 3 times stronger than wood and it will never rot. This product saved me from junking my hull. Now the hull is stronger than when it was new.
I would never think of adding wood back to any hull if not necessary. Why would you add something to the hull that is known to rot????
building boats with wood cores is going to be a thing of the past or at least separate the men from the boys. more and more companies are looking at wood substitutes. Active thunder for one is a completely wood free hull, even in there interior. It is the only way to go.
Check out there web site.
http://www.transomrepair.com
Download there video. It is quite cheesy but you will get the idea. There product has been refined to pour easier since the video was made. it is very easy to work with.