Rachel, I can't comment on modern boat's ice box insulation, but on our old boat - built '66 in Holland - insulation in the sides and bottom of the ice box was rudimentary. There was none at all on the top surface, and that was where the stove radiated it's heat downwards, directly into the area you were trying to keep cool..............! So when I decided to go to a mechanical refrigeration system - belt driven from the engine - my first task was to tear out the whole ice box and rebuild it with "good" insulation. This was a major job by itself, but the end results were well worth the effort. Maybe that is how you have to start too. Then even small amounts of ice will stay for quite a long time (we brought ice cubes from home for the weekend, and many Sunday nights we took ice cubes back home again). Connie