Frank Langer
1984 Ericson 30+, Nanaimo, BC
Brett,Hi Brett, long time ago, I added an inch of foil-face rigid foam insulation to the inside 'roof' of our ice box. Also to the underside of the removable lid. EY had not done this. Makes a noticeable difference in maintaining the cold.
If, perchance, your ice box has an open hose draining melt water (and most of the cold air....) into the bilge, put a cork in it.
Another thing I did, after reading up on heat transfer into these little boxes was to put some thin soft foam "weather tape" on the underside of the lid edges where it rests on the internal flange. That makes a large difference. This considerably reduces the amount of outside moisture sneaking in to condense on the coils and ice them up.
Our '88 model has about 1.5 inches of rigid foam glued to the outside, but like you I have added another inch of closed cell foam to the three sides that I can reach.
It's kind of "a game of inches" where you just keep sealing it better and insulating it better and then...... one weekend cruise you notice that the reefer compressor is running well under half the time and your food is at 38 degrees, ... and.... life is good! The Admiral is happy, and you open a bottle of chilled wine.
Salud!!
Also, to prevent unnecessary opening of the lid to check on the little cheap thermometer I had left inside, I bought a little sender and remote display from Camping World so we can monitor the inside box temp while sitting at the nav table, just like real "yacht owners" might do!
Good luck, and here's to future cold drinks!
There is a product that I saw in a hardware store that was about 1/4" thick and was intended to stick on the inside of an ice box, and provided good insulation. My wife didn't want to give up even a 1/4" of our refrigerator, so we didn't buy it. It might be a good solution for you.
Frank