Hi Monkey,
I have a Citroen C8 2.2hdi manual bought new in 2004 and as far as my own experience is concerned I would have to say avoid unless you wish to spend a lot of time waiting in service reception for it to be repaired.
My vehicle is the most unreliable car I have ever owned and I would never buy another Citroen. Perhaps I have just been unlucky.
Maybe the Fiat variant is more reliable (unlikely imo ).
On the positive side - very comfortable cruiser, spacious, very safe (5* in ncap test ) lots of kit for the money.
The 2.2 is the one to go for if you tow a van as the 2.0 has a lot of car to move especially with an auto box which will sap the power making for slow progress (2.0 jtd auto 0 to 60 mph 16.1 seconds ). I don't think they produce a 2.2diesel auto so you may be stuck with a 2.0.
Towing a 1300kg van I get approx 24 mpg according to the trip computer so i would knock 2mpg for an auto box.
In short, what should be a good car let down by poor reliability.
Best of luck