Installing a Grey tank on a PUP, asking advice

The linked 7.5gal system is nice. I'm currently using a 15gal rolly tank, though I own some 7s so may explore going back to that.

As to the utility if having a built in tank, I have been finding that for weekends, 20 gal is about all the gray I make, and am thinking that being able to just run a hose to a dump station at the same time as I dump the cassette would be handy.

For longer stays or more people, the utility of having it in board is much lower, or non existent.