Don't worry too much. I think that wood is just a backing between the liner and the hull. It's there to give more meat to the thru hull for the fish box. I'd leave the wood there, and just let it dry out a bit. Pull out your drain tube going into the fish box. That is most likley where the water is coming in. pull the tube and let the wood dry out. Then use 1/2" PVC to make a mold for the drain. No more water leaking past any tube. It's an easy fix. The 1/2" pvc will give you an 7/8" hole. no need for the coupler.
how to fix the drain tube