That's a big tank!! How big is your black and gray tank? You should have a monitor panel that you can use to keep an eye on your usage from day to day. I generally make it a point to add a 5 gallon jerry can of water every day and that keeps me in business and isn't a huge chore like carrying 6 cans every 5 days...spreads the workload out. My tanks on the '06 23B are 30 fresh and 22 each on the black and gray.
2006 23B Hybrid with 10k round bar WDH
2011 F150 4x4 SCREW Ecoboost, Max Tow, Integrated TBC, 3.73 LS axle, Firestone Ride Rite airbags.