I have the Barker 42 gallon tote tank being discussed here. We bring it whenever we know we will be camping without a sewer hookup, which is usually 1 or 2 trips a year.
It will work perfectly for what you want to do. Main downside to it is, like already said, finding a place to store it when on the road, and when not using it.
I wrap ours in a large black trash bag and put it in the back of the Jeep we tow. It fits, but barely. Still trying to find a better way to store it. One day we may try mounting it to the rear ladder like was shown on here a few posts ago, just not sure if I can bring myself to trust the ladder for carrying something like that when on the road.