I've kept both petrol and LPG usage (and all car specific expenses (but not shared stuff like screenwash) on both the defunct Bullet and TBE. Obviously, I can't match Entwood's solo MPG figures, unless travelling on works time, driving in my own time returned figures similar to Entwood's towing figures. TBE uses more petrol, as it switches back below 1200rpm, due to knackered LPG injectors.... ...not made my mind up if I CBA to replace them or not.
The reason I went tractor engine this time was simply the lack of LPG in these parts. Currently, on this tank of black blood, its done 569 miles, and 39.3MPG according to the dash (which does seem to lie). But diesel here is 141.9p