Hi Freerunner,
E-Caps (Electrolyte Replacement Supplement) from Hammer Products are the solution. Not just salt but also other chemicals that you need (but sweat out). Take one every hour and no more cramps (well, you need to be hydrating too, but you seem to have that covered).
On the double centuries I ride the ride organizations that put on the rides have E-Caps at every checkpoint (30- 40 mies apart depending the climbing from one to the next). I take two at each checkpoint and since I've started doing that, no more troubles with cramps!
http://www.hammernutrition.com/produ...-energy-drinks
Rick / OCRR