Pace,
Sounds like a great trip and that was basically the plan, although not quite at 200ft... As I said, ATC were very insistent that we didn't route through the danger areas, but were then very accomodating getting us around to be fair. Big lesson was speaking to Brest on the telephone who gave us all the detail we needed for the return and that was the way we routed back from Burgos.
Perhaps we should have been a little more insistent, but on our first trip beyond the Channel Islands or Wales we weren't quite ready to start an international incident without being absolutley sure we were in the right.
Second using La Rochelle or Nantes to split up the trip. If the seat cushions are of 1978 vintage 2 ish hr legs are about enough!