Since Randy's initial post...both he and I have had a chance to do more testing with the ECW GI bag.
I've run a couple of different tests now. Here's a picture of my TrekLight Double with the ECW GI bag thrown inside. All I wore that night was a white cotton undershirt, cotton pajama bottoms, and a pair of regular tube socks...and I was HOT. Never did zip up the bag. I would open it a bit to vent in some cool air. Not sure what temp was that night, I don't have a thermometer, but it was freaking cold when I'd get up to "water the lawn".
First test was with a Blackbird + top cover + ECW bag inside.
A hammock + ECW bag + me wearing next to nothing = success!
If I'm not mistaken, Counselor had success with a Grizzly bag he picked up a few days ago. Maybe he can chime in...
Only problem with the grizzly bag - zipper is on the right . . . for my left entry blackbird it takes some gymnastics to get into the bag . . . i don't mind, just gets the blood going!