Nice one ClimbinArbor.
"An old timer told me in the old days many wore long underwear through the summer to hold the sweat while doing physical work"
That's not true exactly. They are holding the sweat, just not in their bodies. What is actually happening is you are just holding the sweat in your clothes. Here's how I know: Many of my buddies are ex-high-school and college wrestlers and now go to the same MMA gym that I have been going to for three years. Whenever anyone needs to drop serious weight (like all these wrestler kids do all the time apparently), they throw on a plastic suit and jump rope and seriously work out to sweat out all that extra weight in the form of yes, sweat/water. I'm not a physician, but I am guessing the reason more sweat is coming out fully clothed - especially in a plastic suit - is because it is not eveporating and the body is getting hotter and hotter and trying to cool by dumping more and more sweat.
I can't believe the grief those old timers caused themselves, if only they had known a wrestler.
I like the vented pants idea, I would definitely buy something like that. BUT,
"He just cut out the crotch and pockets and sewed in mesh." doesn't that mean your undies are hanging out? I don't think I'd care to much, but clients and my guys might. Guess I'd have to see the venting.
Anyway, I wore pants on a long job yesterday (with a long sleeve shirt too) because every tree had tons of poison ivy growing up it. Never seen anything quite like it. It was almost like a kudzu invasion.