The setup of our current Northstar camper is similar. A lot of fesh water, small gray tank.
If/when you have a cassette toilet, you need to dump very frequently anyway.
And a place to dump is much easier to find than a source of fresh water.
We dump the (usually about half full) cassette daily as well as the gray water tank (using a bucket for the gray water). That way, we always have 2 day reserve. And a half full cassette weighs only half as much as a full one when you take it out. That way, we can stay parked in one location until the fresh water runs out (> 5 days), as long as we have a place to dump the cassette and bucket within walking distance.
Works for us, doesn't work for everyone.
