I'm piecing together a lightweight winter gear list for some northshore minnesota snow shoe trips this february. I'm planning on building a large-ish pyramid type shelter that can accomodate 1 or 2 people with gear comfortably. Right now, I'm thinking of something like a Shangri-la 3 or slightly smaller black diamond mega lite (8.5-8.75 foot square or hexagonal bases, height around 60-65 inches).
I'm leaning away from coupling this with a bivy sack as I like being able to get in and out of my sleeping bag without messing with an extra zipper and also having a floor to spread some gear out on. I'm looking at potentially extended trips with this, and want to be comfortable.
My question is this: for those that have used 'mid-type shelters below treeline where finding some sort of protected site is just about always an option, is a full nylon inner (double wall) necessary, or have people had good success with just a floor or ground sheet? I'm thinking a bathtub floor with 4-6 inch walls covering half of the sheltered space should keep me and my gear off of the snow and block a little spin drift and breeze for minimal weight. I think pitching a large pyramid with a peak vent close to the ground should keep most spin-drift from coming through in the first place. I'd leave a gap between the bathtub floor and the pyramid walls, letting any un-frozen condensation run down to the ground.
Again,if I was expecting frequent brutal storms, I'd make a full DWR nylon inner tent without hesitation. However, I'm thinking that for northern minnesota conditions (sheltered, some snow but not frequent big snowstorms, potentially very cold), the setup described above could suffice.
I'll be using a -10F WM lynx with microfiber shell as my bag (good water resistance while still being breathable enough, from what i gather)