One of things I'm missing here is what are you preparing for? Although we have a 6 gallon tank that uses both electricity and engine coolant, the most we use it away from the dock is rinsing dishes. To my knowledge, no one has ever showered on our boat since it was new. Of course, our deal is different than others. We are in fresh water, our "cruising" grounds work out nicely that we can go from club to club, get free dockage which includes power and water. The previous owner did the same thing. In fact, there are very few places on Lake Erie that are free anchorages in protected waters, you almost have to use transient dockage when traveling. The exception would be at the West end of the lake by the islands.