I have an Eberspacher hot air heater in the van which I fitted myself. I have connected this up the to vans fuel tank. I have a solid metal bulkhead that seperates the cab from the van. This unit draws cold air from the cab area, heats it up and delivers it mainly back to the cab although it does have a splitter to heat the cargo area as well. This can be regulated and at the moment its set for about 20% cargo area and 80% cabin.
I have found that it takes a while to warm the cab up and would imagine it would take ages to warm the van if it didn't have a bulkhead. So as an overnight frost heater then it would be OK.
However, whilst 1/3 litre of diesel an hour on tick over isn't much, it would soon add up over a night, and a month. The fuel consumption figures are given in a medium I can't relate to, but as this is a bigger unit than I have (5kw as apposed to 3.5kw) then I must assume that this unit will use more fuel than mine. As the tank holds 6 litres, you would be filling the tank so regularily it would turn into a chore. As the unit would be fixed in the van with an exhaust hole drilled in the van's floor, fuel spillages would be a common occurrence.
Another thing is that these units take a fair amount of power to restart themselves everytime. Mine draws about 12 amps for a short time with the glowplug heating up, and then about an 1amp on tickover. Mine is wired up to my leisure battery.
Mine doesn't have a silencer fitted, so sounds like a jet engine when it starts and runs - not good for neighbour relations if used at night. There is an optional silencer which i would fit if it was being used as a night heater.
These units were made popular as an aux heater for campervans and Yachts, and BT fitted them into their vans to save the technicians running the engine to heat the vans all day.
It nice to take refuge in a warm van when the weather is cold outside and the dog also enjoys it.
I use an electric frost heater in the back of the van at night as this is must cheaper than runing a diesel fueled heater.
Spruce