Sat at 85 on the dual carriage way it was showing 36 mpg on the computer
My XJ shows around 40mpg doing similar, but Jag fuel computers are like a cheap watch, to the order of 10-15%. So probably very similar in reality
Over the 2 years I've had it, I think my (manually calculated) MPG is hovering around 32mpg - and now has enough data points that a good long, 300 mile 70mph cruise doesn't really impact the overall figure. I think you drive more sedately most of the time, so you might get good figures.
So pence per mile, purely on fuel, its a bit behind the LPG MV6, and diesel servicing does tend to be a little more expensive (and all modern car servicing is, because they all need this new fangled oils and shit - and in your case, probably some pigs piss as well?). I suspect you might gain on the towing side of things though.
I'm always wary of remapping Audis, but that is based purely on the older A4s and their shitty manual chocolate gearboxes that start to melt. So if you go down that route, go with trusted, reliable feedback from people you know/trust, not marketing tosh.