Re: sound proofing
Some FRB builders ( Sea Ray, Intrepid) now incorporate a material into their laminate schedule that converts sound-vibrations- into heat. ( DOnt ask me how). I handled a sample of the stuff and its got the feel and heft of Kraft paper--very thin; yet its silver. I heard some demos at the Miami Boat show and both audibly and via a sound meter, the boats with the stiff installed were way quieter.
Anecdotally, running large powerboats whose engine hatches are either balsa-cored or foam cored are much quieter than boats with solid FRP hatches with equivalent power. Talking big boats with a pair of big diesels. So Id say that maybe a simple lamination of Divnicell or Balsa on the outsides of your well would serve.
This new ship here is fitted according to the reported increase of knowledge among mankind. Namely, she is cumbered end to end with bells and trumpets and clocks and wires. It has been told to me she can call voices out of the air or the waters to con the ship while her crew sleep. But sleep though lightly. It has not yet been told to me that the sea has ceased to be the sea.--Rudyard Kipling