We have elaborated below on our earlier email about improving the refer. Attached are photos illustrating our refer project. It is not a quick solution, but it IS a permanent remedy to the moisture and heat migration.
Photo 1. Shows the lid open. The old, ice-cream-box style lid used in our 1993 IP was discarded in favor of a single piano hinge style that eliminates the weakness of the middle hinge. We believe that newer IPs have already adopted a single-unit lid without a middle hinge.
Photo 2. Shows the top of the refer closed. A butcher-block cutting board was trimmed and planed to serve as strong-back for the lid. The original lid was supported just by a ~1/2" lip. The weight of the new lid would have eventually weakened that small lip. The butcher block is useful for cutting, and it supports the full weight of the new lid all the way around because it rests "on", not within, the lid opening. As with a classic butcher block, we periodically clean it with water and bleach, sand it with a block sander, and apply olive oil to keep the wood from drying out so much it cracks. The inside of the box top has elsewhere been insulated with a matching 4 1/2" of foam panels, covered with fiberglass.
Photo 3. A close-up that reveals that details of the lid with a stair-stepped edge with two large gasket edges. The lid, is 6" thick including the butcher block. The lid touches the opening frame at the bottom of the butcher block, at the first ledge, and at the second ledge. The underlying 4 3/4" of fiberglass lid is not hollow: it is completely filled with foam sheets.
Photo 4. Shows the rear frame detail, and the manner of attachment of the piano hinge. It also shows the top of the insulated, spill-over divider. The divider is NOT fiber-glassed to the sides. It is just set into place and held with wooden brackets screwed into the front and rear sides. By removing the brackets on either side, the divider can be removed to work on the box, if necessary. The wood is unfinished, and moisture does intrude into the wood a little, but only within the box.
Photo 5. Shows a close-up of the upper hole and cover used to control spill over flow. A similar, but larger, hole and cover is situated in the center of the lower edge. The divider contains the air in the left side freezer(actually starboard) just enough to keep the refrigerator side from freezing.
Photo 6. Shows the digital thermostat controller. It cost an extra $250, but it is infinitely more precise than a simple twist-knob rheostat controller. It allows the operator to easily adjust the "set point" at which the unit turns off (say, 18F degrees). Less easily adjusted, but nonetheless under user control, is the upper range which establishes at what point the unit turns on (say, 7 degrees above the lower set point). The bulb of the controller will periodically be covered with ice, which over time gives rise to a difference between the reported box temperature and actual.
Photo 7. Shows an independent, digital, wireless, two-sensor thermometer which is useful for tracking and balancing both sides. It has no control over the unit. The sensor for the freezer side is mounted high within the freezer box so that it reports the highest temperature in the box (which must go no higher than 32F). The sensor for the refrigerator side is mounted at the lowest point in the box so that it reports the coldest temperature achieved (which should be no lower than 33F or you'll freeze your milk, etc.) This thermometer was purchased online for about $20 and includes resettable historical high and low tracking, plus an alarm which can be set to warn of too high or too low temps.
Photo 8. Shows the boat's analog ammeter reading less than 1 amp and proving that the system actually does cycle. Our earlier system, an old Adler-Barbour, never cycled and was a constant draw. We do not have an AC generator and we rely upon solar panels and a high-amperage alternator to maintain the batteries. We have achieved a freezer/refrigerator that makes ice, produces no condensation, and cycles on and off. The system uses more power when it initially comes on, and lower power as it approaches its target set point.