Using a Zeer Pot instead of a Refrigerator

I was reading a woman's dream about become self-sufficient, and she mentioned using a Zeer Pot. Of course, I thought, "what the hairy heck?" but they did a little internet surfing.

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Source: http://en.wikipedia.org/wiki/Zeer_pot:

The pot-in-pot refrigerator, also known as a Zeer الزير in Arabic, is a refrigeration device which keeps food cool without electricity by using evaporative cooling.

It is constructed by placing a clay pot within a larger clay pot with wet sand in between and a wet cloth on top. As the water evaporates it cools, allowing food stored in the inner pot to be kept fresh for much longer in a hot, dry climate. It must be placed in a dry, ventilated space for the water to evaporate effectively towards the outside.

Mohammed Bah Abba invented the device in 1995 and was awarded a Rolex Laureate (Rolex Awards for Enterprise) in 2000 for developing this “pot-in-pot preservation/cooling system”.

From http://www.slashfood.com/2006/09/28/how-cool-is-that-zeer-pot/:

Of all the households in the US, 99.5% have refrigerators. About the same percentage have some way of heating food. We've seen some great gadgets for keeping things hot and cold here on Slashfood, but I want to show you an ancient technique for keeping food cool. It's called a zeer pot. The vessel itself may be third world, but it's playing a timely role in the continuing recovery of northern Darfur and other African nations. Science in Africa magazine states that a zeer can keep tomatoes edible for 20 days, as opposed to two, and meat two weeks, as opposed to a few hours.

A zeer pot is quite simple. It's basically two large earthen pots, one nested in the other. The space is filled with sand and water is added. A damp cloth covers the top. As the water evaporates, the inner pot containing the perishables is kept cool in the same manner that a mechanical refrigerator operates -- water evaporation draws heat from the inner vessel. Water is added twice a day.

Muhammed Bah Abba is credited with reviving (some say inventing) use of the zeer and has his own instructions on theory, application and making one. I am going to make one of these myself and see how long basic vegetables will keep at room temp. You can see from the picture how easy it would be to improvise a zeer with regular flower pots. I will then give it a taste test after one week.

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We definitely want to reduce our carbon footprint, get off the grid, and eliminate using a refrigerator that could break down. I've seen lots of old-timey-type boxes and ice-boxes, but like this idea. When you have all of your food right at your fingertips for harvesting, and a cow in the barn for making fresh butter, you really don't need a LOT of refrigerator space. This sounds wonderful.

I couldn't find any retailers online for these. Questions:

• will any clay pot in a clay pot work this way?
• will any kind of sand work in the bottom pot?
• just a wet cloth on top? does that keep much coolness in? what if you can't re-wet the cloth twice a day?
• as an alternate, what kind of top would you put on... and would it be on both or just the inner pot?

Anyone?