When finishing races my face is white from the salt from sweating: I get severe cramp in most races longer than 2.5 hrs.
Early 2008, I was taking an expensive high5 anticramp drink(which had caffeine in) and it took me ages to figure out that it was the caffeine that was making me worse.
I swapped the anticramp drink for a simple solution of half water, half fresh orange juice and a good pinch of salt and the cramp eased up tremendously.
Two things to point out:
1.I've never liked salt since childhood and have to force myself to have it on chips and wont have it on anything else. So maybe I'm already at a disadvantage.
2. at the same time as swapping my drink, I ran alot of Lakeland races including Duddon Valley, Ennerdale, Buttermere, and when not racing I would be up around Pendle hill on weekends. So maybe the regular and extended hill mileage contributed too.
This year I did The Trog and suffered again but not as bad and now I'm desperately trying to up my hill mileage before the edale skyline and 3peaks comes around.
Fingers crossed.
ps
Ive tried nuuns too but still get cramp, I'm leaning more towards the extra weekly mileage solution.
Hope that helps stef.