I have an option. It may be a bit expensive but it will kill two birds with one stone. A marine diesel heating stove. It heats and also has the ability to cook on it like a regular propane stove. It can also run on kerosene in a pinch. They use hot water coil for heat, it could be a forced air set to run through the bus heaters, or just heating straight off the stove.
Dickson Marine seems to be the best in quality and praised by my boaty acquaintances. They can be found used at boat supply places and on ebay.
http://dickinsonmarine.com/product_cat/diesel-stoves/