This cooling box is for hot, mostly sunny places that are not very humid. High humidity would reduce the effectiveness of evaporative cooling, although air movement might help to some extent.
Windcatcher elements/configuration could improve air movement when needed.
The box needs to be made of stainless steel, aluminum or other metal/alloy that doesn't rust easily, because it should be metal to conduct heat well and we want it to last.
A cheaper version could be made of galvanized steel or using some form of galvanic corrosion protection.
If cooling the room instead of the contents of the box is desired then the box door can be left open or removed and a small fan could be added. The fan could be powered with a Peltier module, exploiting the temperature differential we generated. Or just let the air flow in.