@Altitude sickness - for me Sea Duck hunting was usually in Salt Water and a lot of Fun (we Never lost a gun & safety/life jackets were a top priority).
The boating aspect and being a mile or more off shore is nice part of what makes Sea Duck hunting Fun AND you never know what you’re gonna see out in the Ocean. But you mention an “layout boat” so assuming you might be on a large lake? We never used layout boats Off the NJ coast as hunting in the ocean 1 to 2 miles off shore they are Not seaworthy enough for anything but flat-calm-water…..also Not needed as Sea ducks decoy readily regardless of boat (although a Layout boat certainly never hurts).
Years ago in the early season (Sept./Oct.) I’ve seen dolphin, sea turtles along with the surf & white winged scooter we expected. Old Squaw were usually more abundant in the bays then 2 miles off shore but they showed up as well. Sea Duck hunting was a lot of work and in the Ocean highly weather dependent - winds over 10-15mph caused problems and safety concerns….also very difficult to retrieve downed birds and we didn’t like our dogs in the water in white capped conditions - so we paid close attention to the Marine Weather Forecast before heading out.
I like Benelli and especially the SBE (plastic/ugly) - never minded (or noticed) a few scratches from banging around in the boat. I did always immediately “clean & oil” the gun when I got home - took apart the bolt/trigger guard/spring etc…. It seems the “spring” is most prone to rusting but that’s also easily replaced if needed.
Hope you have a great hunt - it’s really different than any other type of duck hunting. Do they have Eider where you will be hunting? Those birds seem to be extending their range South over the past 20+ years and are now off the coast of NJ.