Ok, so if I'm understanding things correctly (which may be a HUGE stretch!), to operate the hot water heater, I turn on the gas supply, give it a few minutes to get gas in the line, then go inside the trailer and turn on the hot water switch. The fresh water tank is full, and I'm getting water out of the hot water faucet on the kitchen sink. (see pics).
I don't see a way to get to the back of the heater, to check for bypass valves, or winterization switching.
Also, didn't see anything obvious underneath, that might suggest a fresh water drain valve, but I did find two small hoses (see pic below).