Thats weird! I started on Levemir 8 weeks ago, (now on 130 units/night) and I have suffered from leg cramps to the extent that I jump out of bed screaming like a banshee and scaring my partner!
I too asked if this was a side effect of the insulin, but was told it wasn't.
Your solution is interesting as I never add salt to anything and have not done so for many years, The taste to me now is actually off putting, but if its going to get rid of these cramps, pass me the salt cellar!
Stephen