They make what is called a cool vest. Soak it in water, wring it out, and put your outer clothes over it. About $30. Good for 3 hr. + in 100+ deg.
I found a lot of those on Amazon in the $30-$50 range, but they only offer about 11 to 22 degree drop in temp...
I found a product that is Brand Named "Cool Vest" that I am really considering strongly. It uses a Phase Change material that holds the temperature at 59*F for 2.5 hours guaranteed. Spare cooling packs kept in the Igloo cooler can make for a 10 minute stop to replace the ones in the vest when it quits cooling. Even if I don't get the spare packs..... a 20 minute rest stop will cool them down again..... and my trailer has a 48 qt Igloo on it.
I'm thinking ride out in the cool of the morning, about 11 AM it is getting too warm for me, put on the vest, ride until 1:30-2:00 for lunch break... put the vest in the cooler, eat lunch, put the vest back on, and head for the road...
99% of the people on this forum will call this one Over Kill, but you do NOT have my medical problem... my body literally does NOT compensate for temperature swings, and if I get too hot on the highway, and I cannot find air conditioning, I will go into Heat Stroke.
I am looking at the yellow one, yeah, it is $20 more, but hey, if I don't wear my mesh jacket, this still makes me visible.
I think will get a minimum of one pair of shorts to wick the butt dry, and this vest....unless someone finds something else to do the trick??