Well, it looks like my concerns about the new plastic membrane walls creating condensation were unfounded, on average the internal humidity has been 30% lower than the external humidity and there have been no instances of water running down the crown cover or any feeling of damp or ickyness at all.
The average temps this weekend were between 5c and 10c outside and a pretty stable 17c inside, only using a fan heater, I will be upgrading to a 3kw oil filled rad at the weekend. I wonder if I could get through winter with just electrical heating? I will be measuring the electrical consumption and gauging it against what it would cost to heat the yurt using wood or coal. It would be great to leave the fire alone until it gets really cold, it's not the cleanest or greenest way (assuming coal usage) to keep warm.