I am building a small (120 sq ft) portable cabin for a client. I am wondering about the pros and cons of using a 6 gal propane water heater vs an on-demand heater. Someone told me the 6 gal heater means very short/lukewarm showers, others say that won't be a problem. Obviously, the on-demand heater will be considerably more expensive, so I don't want to go with that option unless I have to.