Thanks to all of you for the very helpful responses. I am now exploring the roof tent / trailer / trailer tent options and will report back on progress!

I am planning a "new" (but using a used base vehicle) Land Rover Dormobile conversion for my family and my biggest question is which LWB model to start with. My brief is the following: (i) 6 travelling (belted) seats, (ii) ability to sleep 4 (with the other two in an awning / adjacent tent...