Pop off valve should drain outside the camper if that went off. If you have water inside try the bypass for winterizing to stem the flow for now. If its an internal water line break you'll not have any water, obviously, till you can find out where and fix it. Not fun. Try the water heater bypass first. If it's the tank that should stop it leaking inside. If it's in the hot water line father down the system away from tank it will still leak. Could also be line into system from city water, if you were connected to that. Since the heater had been functioning erratically that could be the problem or a slow leak that finally gave way. In any car good luck to quick fix.