Bear in mind these types of heater require a combustion air inlet and a combustion air exhaust both around 25mm to the outside of the vehicle....
The combustion exhaust gets very hot so needs to be well away from anything combustible....
They also need a circulation (cabin air) inlet and outlet around 75mm.... Warm air into the cabin and a way for cabin air to get back to the heater...
My eberspacher (wouldn't entertain the cheap Chinglese ones) is under the passenger seat box on our Jumbo...
Warm air outlet is out of a vent in the rear of the seat box return air just back via the opening in the seat box.
Well worth fitting combustion inlet/exhaust silencers to reduce noise levels.
Eberspacher fitting instructions here to give you an idea...
https://www.google.co.uk/url?sa=t&sourc ... q9XBY8fOjJ