I read something about some guy out in the frozen eastern step/desert with some locals who simply lit and stoked a huge fire with dry bushes, chucked on lots of stones as it burnt down then covered the embers with sand/soil. No blankets no cover, just lay on the hot ground. The bloke writing the article complained about the heat. The air temp was -35ºC.
Shelter and insulation from the ground are the main considerations IMO. I've slept out in -20ºC with a pit that I'd happily have swapped for two heavy wool blankets. Although I did have a proper mat and some shelter in the way of a cycling cape for my top half and my rucksack for my lower part. Spindrift was an issue on my face at times as I kept popping it out in my sleep for some reason, woken each time with a start as spindrift dusted my chops.
During the night I wasn't warm but I wasn't too cold either, it was the morning that was the tough part, or rather getting up in the morning, thats where I chilled down. Really difficult to get squared away and moving. No frost nip but how I cried, with hot aches once underway. Possibly the worst I've experienced. Thats the folly of youth for you
I really think there's more than something in the posts above that talk of improvising some shelter and using natural material to get a body off the ground.
In times gone by people sleeping out in highland scotland slept on a plinth of heather and slept under a big mound of the stuff, all materials were cut for the purpose. But I'm unsure if it was tied in bundles etc. However it was done it was done in such a way as to shed rain.
In the book "Dersu the Trapper" by V K Arseniev (
http://www.amazon.com/Dersu-Trapper-Recovered-Classics-Arsenev/dp/0929701496 ), Arseniev describes being caught out with his local guide Dersu at the end of a trip, the pair had headed off from the main body of the expedition to take some sightings and bearings for the purpose of mapping the bottom edge of a near by lake, whilst they waited for a train to pick them up on a newly extended bit of the line.
The guide started getting agitated about a bank of fog headed their way on another wise lovely early autumn day. The guide busied himself cutting and tying reed bundles that he in turn tied to the reed bed, adding bundles tied end on together to form an anchored and secure reed mat. The fog turned out to be an advancing winter storm that they survived by huddling under the reed mat for 24 to 36 hours until it passed. A good read that book.
Anyway, an interesting proposition and I'll look forward to hearing how you get on. Personally, I think with a shelter and fire, a thick mat of thin twigs or similar, you'd be fine. My only comparable experience that I can pass on would be to get something hot (food and drink) into yourself before you get up into the cold of the morning.