G1E, the idea of an integrated insulation pad, bag, and reflective/vapor barrier reminds me of the old Warmlite/Stephenson triple, which I'm sure you've come across (maybe even used?); although reliant on materials not esp appropriate to this mission set, the concept and attempt to use offset baffling to minimize loft shift or compression and cold spots seems sound.
Once you introduce the wx extremes of those temp ranges, wind resistance, and maybe snowfall weight for picking a tent system, all hell breaks loose in terms of pack weight to usable volume, venting/condensation mgmt., guying vs self-tensioning. I don't envy you the challenge of design!
As a warm sleeper, I've done well with a -20F (ratings always taken with a large grain of salt, being dependent on pad choice and user metabolism, I think) synth bag and rip-stop/g-tex bivy bag, with a light-wt tarp for heavy rain/snow when needed and when really in bad winter wx, tarping over a slit trench. Able to stay drier than digging a full cave or quinzee. Short-term use only, and the caveat that I hate winter camping...
Does your bag system have the option of mating (zips or hook/loop) two together? It seems you'd maybe lose insulation along the edge to be joined, for the utility of shared warmth (aka 'trying not to freeze to death').
http://warmlite.com/wp-content/uploa...2/bag-Info.jpg
DaveP