I took the "uninteresting" VIN route, trying to follow the ISO standard as much as I could (as I understood it at the time, anyway!):
The first 3 digits give indication of where the vehicle was made; UK vehicles start with "S", so I chose "S". The 3rd digit should be "9" if the manufacturer makes fewer than 500/year, so mines a "9".
Digits 4 through to 9 indicate some general details of the vehicle type, so mine is "RH2B" with 2 other digits I chose but can't remember why (possibly something to do with the gearbox)
Digits 10 to 17 indicate clear identification of the vehicle, so I followed the old Ford method of using the engine number. The 10th digit represented the vehicle model year, so I used the date the bare kit left the Robin Hood site.
It was accepted by DVLA so I was happy