I think Mocoondo, makes a valid point about system use and milage, I tend to forget not everyone uses a MH like I do. In my case, we travel a lot, rarely stop in FHU sites. So in our case, our system use and milage would correlate pretty close. And we do the service. But still in the near future, I will not be to surprised if a heater or fridge lets go. As our milage is a pretty direct reflection of how many nights we have used all those systems.
But as Mocoondo said, a different rig could spend most of it's time parked, with low miles and high use, or high miles and low use if always FHU sites and warmer weather.