I was issued the ECWS sleeping bag kit when I was stationed with the AFNG in Alaska. I used it several times to camp outside, with no shelter except for the ECWS.

The ECWS is cool because it contains three bags: a cool weather bag (rated to 30 degrees), a cold weather bag (rated to -10 degrees), and a gortex outer shell that is close to waterproof. Combined together they rate to -30 degrees. You can choose what you want to hump.
I camped outside several times in Alaska with just this set, no shelter at all, and it kept me warm and dry.
I had to turn in my ECWS when I left the AFNG, but now they are hitting the surplus market. Both CTD and MMS have them for sale:
http://www.cheaperthandirt.com/ZWB144-1.htmlhttps://www.mainemilitary.com/productcart/pc/viewPrd.asp?idcategory=&idproduct=2355Cheaper than Dirt has them for $200 with the compression sack.
Maine Military Supply has them for $175 without the compression sack.
I've seen them on ebay for around $110 (probably stolen), but I was concerned about quality and the ability to return, so I chose a dealer.
I chose MMS for my latest order, because they offer free shipping, so even though I needed to buy a sack, it was still cheaper. I got my ECWS today, and except for one patched area on the patrol bag, it was almost like new.
I bought a compression sack off of ebay for $17 shipped, so I spent total $192 for the bag from MMS + the sack from ebay.
NOTE: Don't buy the compression bags from walmart, they are shit. I got one thinking I'd save a few bucks, but they are crap. I am returning the one I bought and getting a surplus military one off of ebay.
NOTE: Also, beware of ripoffs. Many sites are selling "ECWS Patterned" bags. I'd rather buy a used surplus real bag than a new ripoff bag.