Good batteries, a good glow plug system and good fuel and you 'should' have no problems with a cold start down to 0 or so on a cold-soaked engine.
I've used charcoal briquettes in a gallon paint can before to preheat the engine when electricity isn't available. 2-3" of briquettes in the bottom, punch some holes around the bottom edge of the can, light, and stick it under the rig with a tarp or blanket over the front end to help keep the heat in. Helps if you can get the can bottom off of the snow (a plate works well).
If you have multiple vehicles going, exhaust from another vehicle ducted under helps too (use metal dryer duct).
I've used charcoal briquettes in a gallon paint can before to preheat the engine when electricity isn't available. 2-3" of briquettes in the bottom, punch some holes around the bottom edge of the can, light, and stick it under the rig with a tarp or blanket over the front end to help keep the heat in. Helps if you can get the can bottom off of the snow (a plate works well).
If you have multiple vehicles going, exhaust from another vehicle ducted under helps too (use metal dryer duct).