Brendan, I've had the same concern. I plan to make a down quilt for my wife and I some time this winter, and I considered using Nobul1 for the shell and Nobul2 for the liner, so water vapor would move out more readily than in. My wife dislikes clammy/plasticky liner materials, though, so I bought Nobul1 for the whole thing because I thought it might be more comfortable for her.
I'm considering using a strip of silnylon for the shell and liner along the edges (the outermost 6"), to prevent wetting of the down by contact with the damp walls of the shelter, but I worry about water vapor getting trapped in there. I did this with a synthetic summer quilt I made this year and it worked well.