Interesting! In my search for a new MH I've started to take pictures of manufactures' price sheets and cargo capacity stickers. According to the Winnie stickers, "A full load of water equals 279 kg or 616 lbs of cargo @ 1kg/L (8.3 lb/gal) and the tongue weight of a towed trailer counts as cargo."
Thanks to this thread I now know that, at least to one manufacturer, a "full load" of water is fresh water only (74 gallons), with no water in the gray and black water tanks. If the gray water and two black water tanks (2014 Vista 35F) were full, that would add another 938 pounds.
Is there a standard format for cargo capacity stickers, or does each manufacturer report what it wants?
Be careful about making generalities as far as what constitutes "a full load of water". Almost every model Winnebago makes has a different size water tank. Our 01 Adventurer on the Ford chassis could carry 90 gallons when the water heater was included. The same model on a Workhorse chassis only held 70 galloons.
The Ford chassis had a GVWR of 20,500 lbs while the Workhorse was 18,000 lbs. The real kicker was that the Workhorse chassis was standard. If you wanted the Ford chassis you got a $179.00 reduction in price.