Morden's B is a 2000 Ford Excel and I don't know if engine idling is a good thing or not. Someone with knowledge could answer that. As I mentioned earlier, good battery management and knowing your capabilities is the answer. I suppose if you had charge your batteries in an emergency situation you could, first, just drive around and find a reason to go some place. Or secondly, treat it like you would a generator. When I did run my generator I closed the windows on the exhaust side and did not occupy my B in a sleeping or closed in living situation. With the generator below the bed/sofa it would have been a magic fingers experience anyway. We set up outside and usually our generator running was for a short period of time to brew coffee connected to an AC outlet. Running the engine, however, does not give you AC outlet power so it would only be done for battery charging. But if it is OK to do so, just do so while outside the B.
In our next B (Sprinter) we will have fast idle engine idling capability for up to 2 hours and it will run the air conditioner and AC power with a second alternator and high capacity inverter. I don't anticipate using the feature except in an emergency low battery situation, if ever. And, if so, would treat using it in a similar manner I described.