Dark cold makes me hibernate, too. Seems natural. That's what the dog tells me, anyway.
My van's got insulation, and I got a regular memory foam mattress and lotsa blankets. No heat, though (except when driving). When it's cold, dark, and wet, I still hibernate, but at least with all the insulation, it's like I'm in a warm nest.
Ya, I enjoy hibernating in that weather but the downside is that I can't get any work done on the computer when I need to sometimes.