Brian, I saw your post over on the Hoodlums forum so I thought I'd give it shot!
I'm including more than one picture just to give folks a better understanding what I did. I hope that's ok.
http://home.san.rr.com/wmerrin/Eric3a.jpg
On a recent trip to the High Sierras, a storm was heading in, so I needed a shelter quick. I found this large dead tree and proceded to make it into my shelter.
http://home.san.rr.com/wmerrin/Eric2a.jpg
The tree had a perfect cave type hole burned about nine feet up into the trunk. I noticed that the root structure had several places (holes) that would allow a framework of poles (branches) to be interconnected to form a framework of sorts. After the framework was in place, I gathered large pieces of bark that had naturally fallen off the side of the tree. I used the bark to "shingle" in the opening, leaving a small opening to crawl through. I used a large single piece of bark to use as a "door" once I got inside.
http://home.san.rr.com/wmerrin/Eric4a.jpg
Here's an inside view of the framework and shingling.
http://home.san.rr.com/wmerrin/Eric1a.jpg
After the outside of the shelter was complete, I lined the interior with a thick layer of pine needles.
Even though I included a picture of the knife, I didn't have to use it in the shelters construction. All the materials were within a few feet of the shelter site. I broke off the branches by hand, gathered the bark, and threw in some pine needles. It was very expedient to make, therefor saving precious calories that I would need to stay warm that night
Heat loss through conduction, convection, and radiation were controlled because of the very thick tree material. It rained that evening so the fourth heat loss mechanism, persperation (wetness) was also controlled. I slept very warm and did not have a drop of rain enter the shelter.
Thanks for offering the great contest!
A very special thanks to Wally for scanning the pictures for me!
Good luck everyone!
Eric