Hi
I tow a twin wheelbase Elddis Superstorm (1800KG) and have done for nearly 800miles thus far - even with 3 teenage boys, 5 mountain bikes and food for a week, it still pulled the van up the notorious Telegraph Hill, M5 at Exeter. OK I was down to 35mph, but the 2.9TDi just kept on rolling.
As an aside, I used to pull the van with a Galaxy 2.0 petrol. That used to snake (being 1/2 ton lighter) and I could never get it into 5th - it just didn't have the balls. I finally gave up when it did - stuck on a hill and couldn't get going again!
As for fuel economy, I got (believe it or not) 42mpg for the first tankfull! - OK, I was very careful and ran it at 70(ish) for 300 of those miles, but I did have 3 adults and 3 boys on board!
Hope this helps