I have been doing some tests between a flower pot over the top burner on the stove, an Origo
heater using methyl hydrate, a small 120V oil
That is about the order of heat produced. If you have an inverter
filled heater draws about 500 watts at full setting and less at lower settings. Could be you could run the engine while usinmg the inverter
to power the oil filled heater.
You could have heat real soon with out any modifications.
I run the heater off my 1000 watt Honda generator
. The generator
is $1000- Canadian and very quiet. If you put the generator about twenty feet or more away you will not hear it on a normal day.