The D-Max would be a pretty good choice of vehicle for this task. The three-litre engine is well regarded in the trade and because it’s a little larger (in capacity) than some of its competition, it also has a bit more torque which is great for towing. With a 3.5-tonne towing capacity, it’s also up with the best of them.
As far as fuel consumption goes, you need to bear in mind that even though it’s a four-cylinder diesel engine doing the work, you’re actually asking quite a lot of it when you’re towing a caravan at highway speeds. With that in mind, you can forget about the official combined figure of 7.8 litres per 100km. Bank on at least double that and maybe a bit more, especially if the caravan is a bigger one.