Tugster,
I tow my Bailey Indiana with an Audi A4 Avant 2ltr TDi 140bhp & the difference between driving solo & towing is worlds apart.
When towing, as well as tugging an extra 1.5 tonnes, don't forget that modern caravans are about as aerodynamic as a brick! (does any one rembember the windslammers we used to put on the roof of the car to deflect the wind over the top of the van?) the only truly aerodynamic caravans are the tiny tear drop ones, but hey I'm not going to give up this hard fought for luxury just to be aerodynamic!
Re-mapping the engine is a good, but expensive, option, but i find by sitting in 6th, instead of 7th gear (7speed auto) is the better option, and again, surprisingly it's more fuel efficient to do so, I guess it's because the engine is working more efficiently at the slightly higher rpm.