Food for for thought. My dealer told me they have had a couple of fresh water tanks crack due to folks filing the up and traveling. It was believed that the shifting of the water back and forth caused the cracks.
My thought was okay... sounds like to me the tank should be constructed to handle what it was designed to carry. They say, it was but apparently flex wasn't factored in!
I dont carry full water, not even in the bus I owned. Always filled up when close to destination if dry camping. But, as I said you should be able to carry what it will hold. Some disagree obviously.