I just fill it with 400 qts of salt ice from a local commercial fishing warf, cost me $20 and will last me about 4 days with 60% of it still frozen and the remaining water ICE cold. We only do this on offshore trips, as for inshore, I have a 70 qt cooler that fits perfectly in my big fish well so that works best for me, fish go in there in ice and it stays super cold and never melts between the cooler and fish box insulation. The only way to insulate the cooler would to build a custom piece made of high density foam covered in a layer of glass and gel coat, then plexus it on, it will never come off, will not be effected by water and will keep things cold. down side is cost and time to do so, and that you will loose about 2" of space from the lid down inside the box to make it worth while, this is how most companies build insulation into lids on bigger boats, some mold it in as well but not everyone wants it so this method allows for flexibility. Grady would make a killing offering this as an option, I could see it now.....fish box insulation package $1500....but how many of us would probably opt for it... probably a lot more then you would think even if the price was steep.
