My suggestion? Find another route in cooler temperatures. I tour for fun and riding in 100+ heat is not my idea of fun.

However, I have ridden on tours where we had temperatures in the upper 90s-low 100s with high humidity. What we did was get up as early as possible and try to hit the road as soon as it's light, usually about 6 am. If you leave that early, it is very possible to ride 60-80 miles by noontime. However, that could leave you sitting around a campground all afternoon in the heat.

As others said, drink plenty of fluids -- including some electrolyte replacements. Make plenty of rest stops to replenish water and cool down. When I rode Bike VA a few summers ago, the weather was extremely hot and broke the record high temperature on the second day (102 F if I recall correctly) -- which was also the longest day of the tour. I had planned to ride the century but cut it shorter to about 80 miles due to the heat. I survived pretty well but foolishly passed up the last rest stop because I wanted to get the ride over by that point (about 70s miles). Big mistake. I had massive cramps in my legs about 2 miles past the rest stop and had to sit in the shade under a tree until they subsided, plus I ran out of water.