Ian, Mike and Bill (another neighbour and owner of the gite where we stayed), managed to finish the mobile field shelter in the time available although it was close and they were working up to dusk on the last day. There are one or two finishing touches to add but basically the construction was a success, although we had several discussions as to whether the llamas would actually appreciate it! Here is a picture of the finished item!
Below is a close up of the towing mechanism which was custom designed and hand welded by the man down the road. Its capacity to withstand towing has not yet been tested!