
This jacket is brilliant. It keeps the sun off you while feeling like you're not wearing a jacket at all. I think I'm actually cooler wearing this than I am in a t-shirt; much less likely to burn anyway.
The pants are where I'm having trouble. A few years ago I found the most ventilated pants I could from Twisted Throttle. These Macna vented pants do a great job of running air over my legs, but do very little where I need it most around my crotch. To supplement those pants I got some riding shorts with a crotch pad, but they strangely disappeared, leaving me to ride with regular cotton underwear which is not remotely up to the job.
One of the great things about the convertible Roof Helmet is that you can swing it open for some wind on your face. Even in that configuration the visor covers most of your face protecting you from Canadian sized summer bug impacts. I just wish Roofs were a bit better ventilated across the top (the newer models might be, but they won't give me one to test). An adventure/off road styled Roof with a roomier chin bar and more ventilation across the top and back of the helmet would be a must-buy for me.

In order to keep the dreaded monkey butt from rearing its ugly head during hot weather riding you need moisture wicking underwear. On my long ride last weekend my cotton boxers were soaked when I got back and I was so sore I couldn't sit down. You do not want to get sweaty and wet under there, but your butt is on a black, vinyl seat so it's going to trap heat. I've been looking into options to introduce some air under me. Adventure Bike Rider Magazine mentioned Cool Covers a few issues back, but they don't make a cover for my fifteen year old Tiger.

His other suggestion of the King of Fleece cover follows a popular bike habit of using pelts to separate your butt from unforgiving vinyl. Sheepskin is a traditional choice, but I suspect some of the engineered solutions above might produce better results.
There are various new seat options, but not for my old Tiger, and spending that kind of money on a new seat for an old bike doesn't make much sense. If I'm going that route, I think I'll be giving Bill Meyers a call. A Canadian winter would be a good time to send the seat in.
I'm curious to see how the new undies and pants will do on hot future rides (which are only going to become more common). The old, stiff seat may eventually get some attention, and I have a contact in mind in Bill Meyers. You've got lots of options for finding ways to ride in comfort even in hot and humid weather. Hopefully this helps you find ones that work.