When you are out in Black Rock City desert for 10 days, keeping things cold is a big deal. Having Ice cream after a week is an extravagant treat. Enough dry ice would do it, but it would take a small fortune. A well-insulated cooler would reduce the requirements considerably. I hear the plastic can get embrittled from the cold and shatter. So why not make a special cooler?
Since dry ice stays dry, it does not need to be water tight. That makes it a heck of a lot easier. So the first decision is "how big"? A natural choice is to restrict the design to a single sheet of 4 foot by 8 foot foam board. Then the little challenge is to maximize the volume while using all of the sheet. It is also important to keep the dimensions simple.
These boards come in several types. I chose "Polyisocyanurate (ISO)" type of insulation. ( http://www.finehomebuilding.com/item/4822/which-ri... ). It is pretty rigid and would not need much to keep it together. Home depot had it for about $45.
Step 1: Maximum Volume
A cube would be ideal, but the part plan did not come out very nice. So I settled for the schedule above. I used a big table saw to do the cutting. This gives a great edge, but is plenty dangerous. Please let us know if you have luck with a different saw.
Step 2: Cutting the Sheet
Start by ripping a full sheet to make a 26" strip and a 22" strip. That means you lose a tad due to the saw kerf, but it is close enough. Then Crosscut as per the schedule.
Notice that I cheated a bit. One of the "C" and both of the "D" parts hang over a bit. There is just enough extra above the "D" pair to make this up scabbing on little strips. I used hot melt glue to hold on the pieces and then trimmed to size on the table saw.
Step 3: Assembly
By now you have noticed that each wall is a full 4" thick. So each wall is a stack of two parts. From the photos, you can see that I carefully wrapped each piece in a systematic way to cover all of the edges. I used contact cement to attach "Tyvek" house wrap. This is expensive, but it is really tough, water tolerant and brilliant white. With a little thought, I'm sure you can find a nice way to wrap your box.
I stuffed it full of frozen food, including a gallon of ice cream, and two bricks of dry ice. I taped it closed with blue tape so that no one would be tempted to open it.
The fist time I used this box, I taped a thermocouple inside before I loaded it. After 6 days, the temperature started to rise so we popped it open. Everything was still very cold, but not frozen. So the ice cream was a bust. Maybe you will have better luck! Please let me know.
If anybody cares, I'll record the temperature this year and publish the results. I'd also like the hear opinions on how to stack the ice.