We have a Northern Lite 10-2 CD with 36 fresh, 18 black, and 40 gray. The black tank is usually the limiting one. We don’t use the hot water heater or the shower. We carry 9 gallons of drinking water (8 jugs under one dinette seat, and one under the sink. I don't recall ever wishing for bigger tanks.
Even though our camper is on the lighter side, about 2400 lbs, we prefer a DRW truck for the improved stability when compared with a SRW.
In the time we’ve owned this combination, the camper has almost never been off the truck.