Any experiences...

[Damnitman]

with a sleeping kit comprised of an "elephant's foot" type bag? http://www.backpacker.com/gear_guide_2009_the_north_face_elephants_foot_sleeping_bag_review/gear/12914   I use a Wiggy's -20 (-60 with the overbag) and although the bag is plenty warm, there is a considerable ammount of bulk...I am hoping to drop some of the bulk and lighten things up while I am at it...
I am not going to go with the TNF bag, I actually plan on purchasing the OMM PA-1  http://www.needlesports.com/acatalog/KIMMlitebags.html   I also plan on buying some sort of "backcountry quilt" (probably the MLD 30 degreee Spirit quilt  http://www.mountainlaureldesigns.com/shop/product_info.php?cPath=42&products_id=133) to improve the temp rating of the system...I figure I'm already carrying puffy coats and pants when I ride in the winter, why not put them to use?
 

[Eric]

good idea to go with a synthetic overbag. I've had good results using an old moonstone synthetic over a -20 bag, but bad results with a down one over the same bag - the down froze into clumps after 3 nights. both scenarios were on >1 week trips at -10 to -30 somethin nights without any vapor barrier and sleeping long nights. I'd use the light down one again on overnights but not multi day. my 2c

[Damnitman]

Obviously synthetics are not the lightest or most compact, but they are more resistant to moisture than down...that being said, hopefully with a quilt as an overbag, my sweat will pass right through the down layer as a vapor and the moisture will still condense in the synthetic insulation, where, theoretically, it will be easier to get rid of it.  MAYBE it will pass right through and condense on the inside my gore tex bivy sack rather than in any of my insulation layers. 
I have always recognized down's superior insulation to weight / bulk ratio over synthetics, but have also been VERY hesitant to use it as any component of any winter system.  Alaska can be cold, dry and unforgiving (right where down shines), but it can also get warm, wet and miserable right before it gets cold, dry and unforgiving again.  This is especially true in SW Alaska (Bethel) where we sit directly under a mixing zone of weather from Siberia, the Gulf of Alaska, and Japan (sometimes weather from Canadia makes it down this way, too).  -20f one day, 38f the next and back to -20, all in the course of two and a half days...
And then there is the constant threat of moisture from an unexpected dunk in overflow encountered on our rivers and sloughs...
But maybe, with a VBL Liner in the down bag, and a synthetic over-quilt I can make it work...
If anyone has any experiences with an "elephant's foot" / "pieds d'elephant" / "half bag", please chime-in...I really want to hear experiences, good or bad...heck I might even entertain a few peoples general impressions

Thanks
MT

[mmeiser]

Obviously synthetics are not the lightest or most compact, but they are more resistant to moisture than down...that being said, hopefully with a quilt as an overbag, my sweat will pass right through the down layer as a vapor and the moisture will still condense in the synthetic insulation, where, theoretically, it will be easier to get rid of it.  MAYBE it will pass right through and condense on the inside my gore tex bivy sack rather than in any of my insulation layers.

This is my exact thinking this winter. I plan to use my new 20 degree GoLite down bag with a 45 degree Lafuma sythetic bag as an overbag and an OR Aurora gortex bivy on the outside. Same thinking. Get the moisture to move into the synthetic or hopefully to the gortex.

I may also resort to a vapor barrier in an emergency.

Sorry I can't help you with this elephant's foot bag, first i've seen it.

[DesertDog]

I've seen the Elephant bag, but never used one.  For what you're doing, you would likely want to use it and your puffies, then have another bag around you and the Elephant.  The Elephant's Foot is a half-bag, typically used by mountaineers.  They use it to keep the lower body warm and cinch it around their puffy down jacket, creating a lightweight sleep system.  Ounces and grams are even more important to those folks!

Check out this site:  http://www.backpacking.net/bbs.html

A lightweight backpacking site with plenty of forum areas I frequent under a different user name (jps1021).  A lot of folks with plenty of experience; 3-season, winter trekking, climbing too, that will chime in and give you some great advice.  I'm sure there are a few that have some experience with an Elephant setup.

Had my first frozen-weather experience with a bivy in Oregon last month.  Went down under freezing up near Santiam Pass and woke up to a heavy frost.  Icy layer on top and underneath the bivy, as well as on top of the sleeping bag.  I was nice and warm and dry in the down bag though.  At least in those conditions and for just one night, the bag wasn't wet, just frozen over.

I think what you will find is that whatever you do, if you're out in severe cold temps for multiple days, anything is going to get frozen, even synthetics.  It's just a fact of life in a harsh environment you're talking about, unless your going to spend major bucks on an expedition bag, and those aren't even a guarantee.  Believe me, there are some f'd up stories with lots of Arctic expeditions over the years.