What about future Whey from BN?? Highly diluted obviously.
Or Staminade or similar?? Or both in a diluted mix of water.
There is special stuff Triathletes/Ironmen use, can't remember what it is called, a good mate of mine competes in Ironman Events so I can find out what he uses if you are interested, he buys it on line, he's been doing it for years, he is a machine, rides 100km before work every day then runs 10km after work, swims on week ends, he has a sickness.
He explained to me one time that you need to add something on these long events as just drinking water will deplete your body of essential nutrients and electrolytes that will stop your nerves/muscles firing and you will just cramp up, I have no idea personally as I have never done any endurance stuff, the longest I have ever done is a 10km run.