Paul,
I never actually realised that you posted that diagram.
It all seems perfectly clear what you are talking about now.
(Sorry I don't mean that it didn't before [Linked Image])
If I was the PoCo and the property owner, here is what I would look at possibly doing:

Extend the 3~ 11kV line from in front of the poultry farm, across the road, to avoid the trees in the adjacent woodland and extend the lines toward the property boundary.
From there, have a 1 or 3~ tranny on the last pole of the line and then run underground along the boundary fence.

What you could also do in the mean-time, while the guy is living in the motor-home, is set up a metering/consumer unit on a post (In an appropriately IP rated enclosure, of course) near to the motor-home, so that he has at least some reliable source of power.
It would mean that when a house is built on the property, the mains would simply just need to be joined to an extension of the underground cable and the metering and consumer unit relocated to the new installation.