I don't overnight anymore but There is only one solution IMO for what you describe. We typically fish the west coast off of Auckland. we take two 90 litre chilly bins. One is empty and the other is chocka full of ice. For the three of us we will come back with both bins full of ice and fish. We are targeting snapper when we do this. If you're after bigger fish then there's no going past more ice. hapuku/bass & bluenose spring to mind. There is nothing more important than keeping your fish cool if you want it at its best.

wet sack works well- also boogie board bags (insulated) cheap as chips