erberspacher also do diesel fueled water heaters. Some bargains can be picked up on the German ebay from time to time.
I have just bought a ex BT van, they come come with one of these fitted.
i thought BT vans had the cab air heater?
Thats correct, however the heater is mounted in the rear of the van and ducted to the cab, its a simple job to turn the pipe to heat the the back of the van.
I imagine with the right equipment it could be converted to run a hot water system, although personaly I cant imagine why anyone would want a hot water system! I think they are an over priced gadget with very little worth.