Mad Dog,
I can't help you with the unreliabilty of your fuel meter. I have the pre-digital dash version and the light comes on around the 130 mile mark. A couple of weeks ago I ran to 191 miles and it took 19.8 litres which was cutting it a bit fine with a 21 litre tank, but now I know how far I can go.
To be on the safe side just make sure you fill up by 150 miles.