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.
There are two kinds of boaters: those who have run aground, and those who lie about it.