Thanks for the post Paul.
We plan on camping in the roof tent most of the nights, using sub zero bags with liners.
The plan at this point is to construct isulation panels that will set up againts the inside of the tent to improve heat retention. In addition, I will wire in 12v electric blankets to preheat the tent and bags while driving (switch them on an hour or two before making camp.
The last option is a propane fire duct heater like this one from Adventure Trailers
Hey guys. I'm new 'round here, but a trick I've learned for cold weather camping is to fill a Nalgene w/ boiling water and throw it in your bag before you crawl in. Keep it in there while you sleep. It keeps your toes nice and toasty! Any 100% lexan bottle will work, but Nalgenes are the most popular. Good luck on the trip!!