For anyone looking for an answer . . after detailed searches and conversations with several Insurers I found 3 companies that will consider long term European cover including storage in France. These are Towergate, Intasure and Shield.
I went with the cover offered by Shield, not the cheapest but it was in my view the most comprehensive covering contents, awning and optional equipment fitted such as motor movers etc. and they asked very pertinent questions including what was my towing vehicle, which none of the other Insurers asked about. I hope this might help some-one else out there . . . as there was a few days when I really thought I was boxed in a corner without cover !