For my latest century, which was the Hottern Hell century in Wichita Falls, TX, I hydrated all week before the ride, I took salt substitue pills, I drank power ade, I worked very hard to be hydrated in every way.
I still cramped.
Please note that I have done this all my life. In high school and college I would cramp in baseball or basketball quite often. I played hard, but I would have leg cramps when no one else did.
It is time to turn to drugs, if I can find the correct drugs.