Hi,
I have the air heater only, so not all that familiar with the water coil/blower heat exchange.
Mine circulates the cabin air through the body of the unit, measuring the cool intake against the temperature setting on the control. If the room is warm, and the control on a low setting, the heater will slow down the air fan and slow the impulse fuel pump so that it goes into 'cruise' mode. It can even turn off for a while, with a very slow draught of air drawn through the heater so it knows when to warm the glow plug, pump fuel and bring the air fan back up to speed.
Open the door to out side and let in a draught of cold air, and the thing springs into gear very quickly. It can seem quite busy at times.
Now if you changed the plumbing around a bit, so that only outside/fresh air was drawn into the unit, this would stay at out side temperature and never be warmed by the heater.
I haven't done it but I suspect the heater would not cycle, just run flat out, or maybe on a low setting run continuously at a slower rate.
It would be something to check on with the water/air heater models as to whether they are designed for fresh or recirculated air, and how or even if they will adjust to a warming ambient temperature in your camper.
cheers