What we are looking at is the Propex HS2000
This runs on Propane or butane.
If you have gas currently you just plumb it in, if not camping gaz is a good solution as it can be got in hundreds of countries and is nice and compact
It runs on a thermostat with options from 0-30oC
The blue one is what were going to buy
more info here
http://www.propexheatsource.co.uk/air-heaters.php
The air inside the bus is heated and circulated and never comes in contact with the exhaust air
Installation requires 2 holes to be drilled in the floor of your bus to let fumes out and air to burn in.
There is extra kits available which enable you to intergate this system into your standard heating so u will have instant heat at your windscreen demister and the front of your bus. about 40 euro
Also available is a 7 day timer which will automatically turn on and off the heater the same as your house heating. about 90 euro
These can be bought outside to this bulk buy.
Depending on your bus there are a choice of places to install
under the bench/bed box
In a cupboard area