Insulation
Tom,
You are most likely loosing heat through the engine room bilge which may be under the box where your shaft runs through. with decks up you should be able to get a good look at the entire build and if sides are well insulated maybe you can place in a 2" piece of insulation in bottom and glass a piece of composite or marine plywood tight over that. You may loose a little space but hold ice. Otherwise I like the insulated bag on bottom idea.
Tom,you also just gave me a great idea, I have a storage box on forward starboard side holds soap, bleach, bilge cleaner, junk, more junk etc. I need to cut it away to remove my fuel tank and it does make a great seat for those older anglers we get on board. I may convert this to an insulated box to hold ice or just remove it and place one of those high end coolers like an Icy Tek style there. This will free up some space on deck and still provide me with a spot for ice.
Dave
Dave