I have been told that under the bed there are a couple gate valves that will stop the flow of heat from the engine to the coach's heating registers. I have an AquaHot, not a Hurricane. It is heated by engine heat, an electrical element, and a diesel burner - three sources for heat - which can all be on simultaneously, or any combination. All three sources will heat fresh water for sinks and showers, plus heat the coolant solution for circulation into the various zones' floor heating registers. My coach has four heating zones - living room/kitchen, bathroom, bedroom, and basement. Each zone has one or more heating registers. The AquaHot also has the capability to send heat to the engine, known as the Engine Preheat system.
In the summer you don't need, nor want, additional heat coming from the engine into the living areas of the coach. So, I would guess the summer position is off. In the winter you do want engine heat to help warm the living areas of the coach, especially while traveling. So, I would guess the winter position is on.