My money's on Grampy's advice:

"To stave off future episodes of nocturnal leg cramps, consider the following tips:

Drink six to eight glasses of water daily. Doing so will help prevent dehydration, which may play a role in the cramping. ..."


It's perhaps just a theory, but I'm convinced most of us are simply more dehydrated than we think we are. I used to suffer from the worst cramp dances at night, but since I doubled my water intake I have never ever had a recurrence.
Hey, you've got nothing to lose: even before purchasing supplements, try one ride day where you guzzle water and electrolyte drinks like you're on shore leave. Remember not to count anything with caffeine as these tend to be diuretics. Dollars to donuts that'll have you sleeping like a baby. (Until you need to use the toilet at 2:30am, which will feel like a stroll in the park compared to waking up at the same time in a world of pain.)