Hi Alex,
I've been following the scope insulation threads with interest and I plan to add insulation to my C11. It already has a carbon fiber tube so with a layer of coreflute it should stay nice and warm. I have a solid, flocked dew shield which I also thought to insulate but your fan idea is causing a rethink.
Anyway, about refractors, sort of. Attached are some photos of my Quest 15x80 binoculars with their jackets and dew shields. The jackets are wall insulation and the caps are pie tray grade aluminium reinforced at one end with a slice of cardboard tube and at the other with a section of a tin can (pre ring-pulls). The inside is painted with some heavy black goop which, given my old bloke's employment, was probably used in the automotive trade. This has kept the binos dew-free since 1984. Is there nothing new under the sun?
I don't know how I came up with the idea but I doubt it is mine. I used to read S&T so perhaps there was something in Gleamings from ATMs (any time from the late 60's to the early 80's).