Just got back from a 6650 mile trip out west on my GS. I used the LDC, Under Armor Heat Gear, and Wal-Mart "Starter" brand undies. The LDC are the hottest of the group. The Under Armor and Starter were about even as far as the heat goes. They were both much cooler than the LDC. The Starter brand felt the most comfortable and pulled the moisture from my backside the best. The LDC felt clamy every time I wore them. All wash easily at the motels. The Starters dried the fastest. LDC $50 a pair. Under Armor $24 a pair. Stater $6 a pair. A no brainer for me in the future. Just my 2cts worth.
None of the motorcycle stores in my area stock evaporating cooling vests, so I am going to try soaking an old flannel shirt and see how long it will last.
It has been many years since I filled my boots with water in the desert southwest, but that is also an option.
R1200RT. Previous K1200RS, K1200LT, R80RT, R100R, R75/5