Fleetrite ELC. Its good for 300,000 miles. But of course I would still check it once inawhile just because. And I agree with DAVE 100%. You DO NOT want a total filter, just that one that catches a little bit each time around. eventually you will get to all the coolant. But then Im anal and I check everything once in a while. Just to try and stay on top of things. Hell half the fun ( for me anyways) is working/ checking things on my truck.
Like I saw somewhere: When you turn on your truck, does it return the favor? HAHAHAHA
On EDIT: What does distilled water cost? 75 cents a gallon? It damm sure wont hurt anything to use it, and looks to me like cheap peace of mind.