Water Wetter has lubricants in it, too. If it doesn't get below freezing that much where you are, you can run distilled water with one normal sized bottle of water wetter, and you'll be fine. The distilled water won't hurt anything, even by itself, but it can boil over once the thermostat spikes over 212F. I'd reccomend using some pre-mixed 50/50 coolant (actually if you're anal, HD actually markets a REALLY good 50/50 coolant that has all sorts of lubricants and stuff...but it's like $20 for a gallon). Then dump a bottle of Water Wetter in with the 50/50 mix to top it off. Can't really do better than that for the street. But yeah, definately don't want that stuff freezing overnight.
I have your service manual kicking around here somewhere in PDF...I'll see if I can't find it for you...it has breakdowns of the coolant system so you can see what's what.