Hi Francis
I used to tow with a 406 Estate and found it to be an exceptional tow vehicle with a caravan about the same weight as yours.
You say that you never exceed the 'limit' but what 'limit' are you talking about ? I always used to aim to get 75 to 80kg noseweight which in theory for a 1400kg van is very slightly under the 'recommended' 7% figure which would be 83kg (7% of 85% of 1400kg = 83kg). With this loading I got very little tail end sag.
One thing to consider of course is how much weight there already is in the boot. This soon mounts up so I always made sure that some of the heavier things, such as the awning, were in front of the rear axle. Unfortunatley this is not so easily done if you have passengers in the back.
Sorry I can't be much more help but just thought it may be worth checking on the actual weights being applied to the rear of the car.
John M