It sounds like you have the hydration and mineral angles covered. How about stretching and massage? Both can relieve tightness and enhance circulation.

I have been using The Stick for about a year to massage my calves, feet and hamstrings after a hard workout and I feel like it realy helps. Much more effective than hands alone. I used to get nocturnal cramps just like yours and I have not had them for a while. I can't give the stick absolute credit for that but I'm sure it doesn't hurt.
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If you only travel on sunny days you will never reach your destination.*

* May not apply at certain latitudes in Canada and elsewhere.