I don't have a black water tank, so that's not a concern. Gray water tank is 26 gallons, fresh water tank is 12 gallons. I very seldom connect to city water, I think I've connected 3 times in 6.5 years. I can tell about how full the gray water tank is by how much fresh water I've used. I can look at the fresh water tank to see how much water is in it.
From experience I know that after about 4 days when I've had to run the furnace
in the morning, I'll need to charge the battery
. That and I have plug in meter that tells the charge. The only time I missed on the battery
was when the temps dropped into the teens then to single digits. The battery ran out around 5 am. on the 4th day. Now I charge it a bit more often, depending on the weather. I have a solar panel
that I use to charge the battery. Out of the past 500+ nights I've probably plugged in about a dozen times.
Week-end trips I don't worry about any of it. I leave home with a full fresh water tank and enjoy the trip.