I never tried the ice coolers (but I suspect, the ice wont last long on a hot day), but the plain water swampcoolers do work. I've been using them in my van for the past 4 years. I build my own to test them out and see if they would actually work. You can find directions on the internet to build one, the burningman bucket design is the blueprint that people use in there designs.
I build one using the bucket design but it leaked water all over my van. I had to drain it everytime I moved the van. I also tested all the available evaporator pads, aspen/dura-cool/celdek. The aspen was messy to work with and imposible to cut to size, so it was a no-go, the dura-cool was easy to cut and inexpensive but it was not effective in cooling and it clogged up after 3 months of use and lost efficeincy. Celdek was what worked for me, it's thick cardboard easy to cut with a hacksaw and never loses effieciency, its suppose to last 5 years. I had swampcoolers going on 2 years using the same celdek. Swampy.net uses a special pad that soaks up the water and doesnt need a pump, but the pictures I seen look more sponge-like similar to the dura-cool, so it will clogged up, in there website they state it will last for at least several hundred hours. Looking at pictures of the inside of a swampy, I would be hesitant to drive with one full of water. All the evaporator pads were thin, less than inch thick except for celdek which is 3 inches thick.
Using a large plastic tupperware will make a good swampcooler case, put a divider between the lower water section and upper fan/evaporater section, this prevents water from sloshing around even when the van is moving. I put a drainplug to drain water every once in a while to clean out, as far as fans I use the 120mm cooling fans, they are loud but they put out alot of air for the 1.5 amps they use, putting a 12 volt pwm speed controller, lets you throttle the speed up/down. I also used the bigger 10 inch car radiator electric fans (about 6 amps). My current swampcooler uses 2 x 120mm fans about 3 amps of power with both fans running.
On a hot day I might go through 4 liters of water, so the water use is not that bad. I've encountered some very hot humid days, and while the swampcooler lose alot of effieciency, it will still put out cool air. If I turned the water pump off on a hot day, the air coming in will be like being next to a heater. On the humid days I was glad I had a swampcooler instead of just a fan. I never needed more than one, but I do believe building a large swampcooler with maybe 2 large car radiator fans, might be very useful in a humid environment. Amp use will be many times lower than an AC.
