fish-on
20-30 gals of water seems excessive. I have heard from others that the live bait well might be the culprit? If the top underside is not glassed or sealed in some fashion the water weeps over and into the bilge. Some thing you might want to check.
Now, water in the foam in the stringers tells me there is a crack or an opeaning somewhere that water is getting in.
Q. Are BOTH stringers wet and can you tell if it is salt or fresh water that is coming out when you drilled the holes? I hate to say it but these problems you are experiencing sound serious