Are you looking at 110 Volt or propane
fueled? Many restaurants and service stations use the electric ones in their restrooms. Some fancy horsetrailers have propane
ones for their tack rooms and horse cleanup. The propane
one we have at home functions well enough for kitchen and one bathroom use. We've added a larger one for a second bathroom and laundry which is about 95 feet away from the original. The problem with the ones we have at home is their size. They are physically too large for our RV's. They might work with a large "sticky" which might have room to spare..
As I see it, you are stuck with needing hook-ups all the time, going without hot water, or using the multi-fueled tanks with which most of the newer TT's are equipt from the factory.
You could fire up a generator
whenever hot water was required, but your campground neighbors might not appreciate your needs. Even with a Yamaha generator
as quiet as mine, I don't operate it past sundown.
P.S. Check out what Mike found! A bit pricey @ nearly $900, but with a wind kit and cold weather kit your hot water problems would be solved.
Maybe someone else has discovered units which I've not seen, but those are my experiences.
& Ann K.