Re: 1979 Bayliner Mutiny
Welcome to iboats!!!
Some people have installed plastic type closed cell foam, some have used dynomat, others have used 1 inch foil faced hard insulation board (from a box store).
Just make sure whatever you install will stay tight and secure with adequate adhesive so it does not fall into the I/O engine.
Make sure it has proper clearance too. Do you know what was in there before?