This past year, I got totally frustrated with our OEM under settee freezer. It was so poorly insulated that food thawed if it was against the wall of the box. It consumed huge amounts of power. It was just terrible. The freezer is critical for us. We are full time aboard on our boat, and we much prefer remote locations. So food storage is important. In addition we need a place to store the fish we catch. A crappy freezer was not something we wanted to live with.
The poured foam factory insulation was of good quality, but was completely exposed to the air. Even though it was nominally "closed cell" foam it was FULL of water from 25 years of condensation. The foam thickness was also marginal for a proper freezer, even assuming it was water free.
We took the whole thing out, cut it apart, threw out virtually everything, and started from scratch. Using Panasonic vacuum insulating panels I built a completely new box. 4mm epoxy coated plywood as the box and with a double sealed lid. The design was a challenge because the vacuum panels are available in a very limited set of sizes. Many design iterations were needed before it was something I was ready to build. A one inch thickness of these vacuum panels is equal to about 10 inches of the best poured foam. I couldn't quite come up with a design that was 100% vacuum insulated, but pretty close. In most places I used a double thickness of 1/2 inch panels just to guard against a failed vacuum panel. Panasonics specifications say that they expect at least half the insulating capacity to remain after 12 years. I'll take it!
The end result has vastly exceeded our expectations. For the first time--ever--we have gone two days without running the generator. The seal on the lid is so tight that even after after 6 months of normal operation there is NO frost on the evaporator. Seriously. None. I have no idea when we will actually need to defrost this thing. A year? Two???
My best guess is it uses much less than half the power it used to. Even though the temperature in the box is higher than it was formally set to, nothing ever gets soft, much less thaws. All this, and because of the improved insulation efficiency we have ended up with a much bigger usable volume of freezer space. Since freezers are the biggest power suck on our boat--by far--this has had a huge positive impact on our power budget. Win/Win/Win
It was NOT an easy project, but it seems to be 100% worth the hassle. It is also not risk free. I only have the specifications to believe that the vacuum panels will last a reasonable amount of time. If they fail early, I'll have a lot of work to redo. Call back in five years...