The water heater arrived today. It's a Gasland BE158 on-demand heater. With 8 people needing to shower an on-demand heater was the only way to go. I got this one specifically because it will function at a low pressure and low gpm (gallon per minute). Designed as a portable unit but lots of people will install them in a "well vented" RV. Unlike other portable units this one will work with a short length of exhaust pipe vented to the exterior. The ignition is done with 2 D batteries so no electrical draw either. Best part is that it was only $129 from Amazon.