All batteries replaced and software updated but still losing 10% every 2 days when van is not in use

[WelshGas]

I also have the PHEV but did not experienced the heater yet. Let me ask 3 questions: is the corner gap below the fridge the only place for the heat to come out? regarding the exhaust coming out I assume this is quite toxic to breathe while sleeping....? while in camping connected to mains... is there also a fuel consumption?

I'm not sure you understand how the Parking Heater, petrol or diesel, works. It is basically a heat exchanger. On one side is the fuel burner that takes air from outside the van and exhausts the combustion gases outside the van. On the other side of the heat exchanger air is sucked in via a vent inside the van, heated and vented back into the van. The 2 streams of air never mix so you won't be breathing exhaust fumes.
The Heater manufacturers state fuel consumption is about 0.3 L/hr on maximum. In normal use about 0.15 L/hr.