Richard: Does 300 miles to a take sound normal? I know you run LPG but thinking you must have done the odd full take of unleaded when you are out of LPG?
I think my fuel gauge has only ever got above half full about twice is all the time I've owned the car so have never run on a full tank of petrol. The petrol in the tank is regarded the same as the spare wheel, for use in emergencies only and for as little time as possible. In fact, I've worn out the track on the sender at just below the 1/4 full mark so it either reads below that or above it, when it hits that point it drops off the bottom, the low fuel light comes on and the dash comes up with Fuel Gauge Fault. At that point I bung another 10 litres in just to move the sender (and freshen up the stale petrol).
However, it's a 100 litre petrol tank so that is 22 gallons, 300 miles on 22 gallons works out to 13.6mpg. A bit low but with a twin axle caravan that is going to be higher than the car and being driven with the revs kept down, probably about right. Use Sport mode and give it some revs, travelling slower isn't the most economical as the revs want to be above 2,000 rpm.
Since I changed my gearbox, the new one changes up at higher revs than the old one did and my economy has improved as it is keeping it in the power band more.