Hello, my name is XXXXX XXXXX I will try help you with this.
This is most likely to be emissions from the exhaust.
It can appear oily as it will contain some unburnt diesel as well as soot, carbon etc.
If the DPF is working ok and you are not using significant amounts of oil then don't worry about it. The only reason you are seeing it is because the caravan is there. It would be going into the atmosphere normally.
You wont be able to solve this.
The best I could suggest would be some sort of deflector on the exhaust tailpipe.
That's what others have been doing.
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