We’re all different, so that means what works for me will not work for you. I am in pretty good shape right now, but yesterday was a hard 125 miles in higher temperatures. I had some minor cramping that I controlled with electrolyte tablets.
I absolutely have to have electrolytes in any fluids I ingest or I get stomach upset. If I really let things get out of whack, I start to cramp. I suggest not drinking any plain water, always something with electrolytes in it. I carry electrolyte tablets (Saltstick) for if I start to feel crampy or I feel nauseous. I have also just used convenience store salt packets. I think I will probably switch to salt tablets (plain NaCl), because they work and potassium is not good for me. A potassium-rich electrolyte tablet can actually burn your stomach. I still carry some plain water, but I almost never drink it. I use it to rinse my mouth and dump down my back.
Last night after the ride I started cramping in weird places, like my shin. I feel confident there was no shin overuse during my ride. Grabbed some salt and it all went away instantly. I also find that if I start cramping, I can put an electrolyte tablet in my mount and the cramps disappear. This suggests to me that there is an autonomous body response that we can control through subterfuge and placebo.