I still tow with a 2001 Nissan Terrano TDi with a simple indirect lightly stressed 2.7 litre diesel engine.
It only produces 125 bhp but tows a 1600kgs caravan just fine returning 23 mpg.......it will run just fine on any old diesel fuel so it always gets the cheapest available.
I have owned it from new ..........it has just clocked 153000 miles and all maintenance has been carried out by the owner.
My concession to the environment is to use a Ford 1.4 TDi for all non towing duties.....this returns a minimum of 55mpg.