For extreme hot weather or desert touring, I was thinking of putting one t-shirt inside another, and sewing them together with a circuit of small diameter vinyl tubing in between. Then circulating cold water through the circuit from an ice chest with a small DC pump.
is something similar. With just the back pack you have a two hour (one full fuel tank run) "charge" time. You need to wear a leather vest over the"cooling vest" to keep the cooling effect in. It really will take the heat away from your body. When temp's are in the upper 90's to low 100's it will feel like 60 degrees under the leather vest.
Hey THAT is a pretty cool idea. If I was riding in hot weather all the time - I'd go for that. When we rode that last 6500 miler it was during the bad heat wave in the Northwest US. We had our first 2 days in the low 100s F then a break. Then we had a day of mostly the 50s and 60s F along the coast followed by our worst day of the trip heat wise - an entire day 104 - 109 in Columbia River Valley.
Some observations -
My wife - who likes the heat (I hate it) had a worse tolerance than me. She actually started to show signs of heat stroke as we rode getting red, swelling, feeling faint, etc... We got her back to the room and I happily went about gassing up and checking tire pressures, buying groceries, running errands. It seemed that me - VERY well insulated - could tolerate the heat better - or at least showed signs that the effects were delayed.
We have the Fieldsheer Motomorph jacket and it served us very well in temps from high 30's F to 109F - the mesh really helped and the rain liner worked great in 3 days of rain and hail in South Dakota and Wyoming.
I commute out here on the California coast this time of year in 50s and Fog in the AM andin the PM anywhere from 50s F to 90F - I use the mesh with the wind over-panels on most commutes and zip them off in the 80s.
On our trip once, I tried wetting my shirt - it worked really well with the mesh jackets. Penny did not because it would have made her too cold. One thing to note is we both "packed light" by using those modern "moisture wicking" type materials. We both buy these inexpensively in Walmart. I pay anywhere between $3 and $11 for a shirt depending on how early in the season, if it has any "styling to it" and long sleeve vs short sleeve. These work VERY well with the shirt wetting. In fact, the reason I didn't wet my shirt more was that just sweating kept me cool with these shirts - BUT I had to drink a lot of water (which I would do in hot weather anyway).
These methods work well for me and the occasional trip in the HOT weather. I would definately try this "Veskimo" if I did daily commuting in like LA or Phoenix though.