Again, I repeat myself, it is sheer masochism and machismo to contemplate doing such a trip in December-Jan. Late Feb thru early April offers more moderate temperatures (still well below freezing), much more daylight and better chance of assistance and survival if there is a breakdown. No matter how much prep one does, exposure of yourself and vehicles to possible -50 to even -60C temps is just asking for trouble in a big way. Do you have any experience in vehicle dependant travel in even -30 to -40C?
Charlie
Unimog U500 with Unicat camper; diesel BMW X5 35d, diesel BJ40 Landcruiser and diesel M37