Interesting point. I too have been thinking about how most thermal kit and wicking kit seems to be designed for people generating muscle heat. As bikers however, in cold conditions we need something that will keep us warm/dry even if we're not ourselves generating much heat. In cold weather, given that we are sitting right next to an electrical system, electric heating seems the way to go. Even if it is more complex and therefore less desirable than, say, merino underwear. I would have thought electric gloves would be a good idea for driving an open buggy. I know nothing about snowmobile kit, but that would seem like an obvious solution.

The other side of the coin for bikers (or open buggyists) is coping with hot conditions, where it is not our bodies that are hot so much as the surrounding air. But that's another story, and not relevant to a trip to Siberia/. I think more use could be made of polymer crystals. Just found this though Motorcycle Cool Vests and Heated Clothes But I'm off topic.

Last thought, could you not home-make some sort of bag that you could sit in covering your whole body up to your neck? That would keep a lot of crap off the rest of you as well as keeping you warmer and drier.

Great idea for an adventure BTW, I have a mental image of you speeding across a Mongolian plain, kicking out a plume of dust behind you. Fantastic.