I purchased this - https://www.amazon.com/dp/B000C77UYA It's an 11gal tank but is much more compact and fit perfectly in my rear drawer/cupboard. It lasts an incredibly long time and is pretty simple to refill at any propane fill place. It's expensive but it can fit places easily in a van build. I tend to use between 2-4 gallons of water per shower depending on how luxurious I'm feeling. The propane has last for many many full water tanks and barely seems to even be affected by showering to be honest.
