This topic is discussed at length at the Yahoo Groups Mainship site.
FWIW, ours has no foam or other filling. There is a transom thru-hull. We removed and glassed over the trim tabs a couple of years ago. We have two round access ports, and I periodically (6 months) use a shop vac to extract several gallons of water, coming from I don't know where. Someday I will open it and try to find the where the water is coming from, perhaps add larger access ports and a bilge pump, but, so many projects, so little time and money.