Thanks for the ideas guys. I thought the rough sketch might help you visualize the situation a little better, although as I said, I didn't get the scale quite right so the 3-ph xfmr feeding thr farm is somewhat farther away than the drawing makes it appear.
Bringing power along the road frontage would undoubtedly be the best in many ways, but unfortunately that's the original option which was quoted as "Somewhere in the region of £20,000," which is why we were looking at the other possibilities.
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's not actually a motorhome, but a "caravan" (US = trailer) like the type you find on holiday sites here, although that's of little consequence as far as the power is concerned.
Your idea is roughly what I had in mind, though with the meter at the far end and a sub-feed up to a weatherprrof distribution enclosure. There are already some barns and other outbuildings up near the road as well, so I envisaged small sub-feeds to each of of those, plus a feeder to the existing mobile home until the house is built.
Anyway, the owner's plans are on the back burner for a little while now while he decides what to do, so there's nothing else I can do for the moment.
