When shopping for our 5th wheel anything with less than 75gal FW tank was crossed off the possibility list. This cut the pack down considerably.
At the time the few offering decent tankage were Mobile Suite 100gal, Carriage 100gal & Alpenlite 100gal. These days getting a large capacity tank is tougher than ever. Builders seem to think that nobody wants to dry camp in comfort. We do. We go to things like bluegrass festivals, short track racing, Albuquerque Balloon Fiesta, trips to Alaska etc. all requiring multiple days 'on the hook' dry camping.
You don't have to fill that tank but when you need the capacity it sure is nice to have it right under your feet.