I thought I'd share this picture with you. I have a 2.5kw electric heater in the boat. By mid afternoon the roof looked like this. The heater is sufficient to keep it warm enough to comfortably work inside.
You can clearly see where the roof bearers transmit the heat into the roof. Just goes to show how well the insulation is working. I am puzzled as to why there is no snow on the outside of the handrails as there is exactly the same good insulation under all that area.