All of my saddles are slotted leather and I wear 2 layers of Lycra with no padding whatsoever. 100 mile days are not a problem.
This all came about while riding the Tour Divide a few years ago. I got a severe heat rash that made it impossible to sit on a bike seat. The kind where you almost scream when it gets wet. In the postmortem analysis, I determined that sweat going down my back got into the padding and made a super saturated hot salt solution. When I ditched the padded bibs I started to feel noticeably cooler on rides. For long rides, I take a teri cloth rag folded into a vee and put it at the base of my back.
Last year on the Tour Divide, I had no hear issues at all. There was a minor blister by that was because I adjusted saddle tension a bit more that I should have.