Paul E, That's awesome. That's pretty much exactly what I'm planning on doing. The idea being the sindle layer and drawstring would ensure that the quilt is drawn well under the air mat to make it air tight.
I figure the drawstring might even hold on the hood and would make the quilt zipperless and seamless since a cord lock could just be undone to allow me enter and exit the bag.
The hood would need some extra material though I'm thinking to allow for twisting and turning from side to side 35-45 degrees since the bag doesn't turn.
Even your temp rang sounds good. But I'm planning on using a vapor barrier and bivy as well in the extreme cold, which will hopefully take me down to zero if need be.
I may even use it inside (if I can fit it) my 40 degree summer bag if it'll let me travel with it in the winter.
I'm looking for maximum versatility. So I'm going with a holistic / sleep system approach.
Being able to opening it up flat in the summer is another good option.
Will probably design it around my Exped Air mat and hope to make it so it'll handle a wide variety of matts so I can use it with a DAM (down air mat) in the winter.
I.E. one option might be to use a thin thermarest with the quilt, inside a vapor barrier… this whole thing surrounded by another light outer 40 degree bag, on top of a z-fold, and in a bivy on the snow. Not sure what that'll get me down to, but it should be quite cozy and light.
BTW, You're not this guy are you: http://ultraliteskunkworks.blogspot.com/2009/02/cuben-fiber-climashield-xp-sleeping-bag.html
I guess he used Cuben, pretty unconventional for a sleeping bag. But heh, for fall and winter use it could make a LOT of sense. It is in it's own way it's like having a vapor barrier built in and it provides a lot of protection from moisture.
BTW, I would absolutely love to see pictures of your quilt, especially, especially if you had patterns or sketches.
I'd love to see what the single layer bottom looks like and how the drawstring and straps draw it in.
p.s. much thanks to that blogger, before seeing how simple it could be it never occured to me I could make a decent sleeping bag with my sewing skills. I had always figured it'd have to be down and hence would need all sorts of complex baffles. Using Climashield XP came as a revelation to me. Not even so much as a zipper or single baddle or seam is required across the whole top. This should gain back some tremendous advantage over the conventional down sleeping bag design.
The only… only complexity is the hood. Indeed I could use a down parka hood, i've seen it done, but I'd like to ave it integrated. I was thinking of trying what I call the "soap on a rope" aproach and have the quilt drawstring underneath be the sole connector for the hood, thus pulling it down under the pad and yet with the release of a single cord lock being able to push it up and pull the quilt out from under the pad.
Curious about whom else has done this. As I've realized with any good idea… if it is good then someone has to have tried it before and probably more then one.
So far you're the only person I've found mentioning this integrated quilt / DAM approach. At least that's what I'm calling it for the purpose of starting a bit of a meme and trying to find others who've been thinking about the issue.
Right, so, the key is finding out what wing or butterfly pattern is going to be best for pulling the quilt under the pad. It may even be asymetrical, i.e. only pull out on one side.
Secondarily there's the pattern for a hood, I may have to invent that from scratch.