Of course I used a sleeping bag. Don't be silly:-D! I meant that I did not use any other ground insulation other than my DM7. I do not have any experience with the DAM, but others have posted about its similarity to the Exped line of inflatable pads. The key differences are that the DAM is made of what many have described as cheap pool float material but it is thicker than the DM7 and uses a higher grade down insulation. I would swear by my DM7, and many others who own this pad have also commented on the durability and warmth derived from using this pad. My bag of choice for weather down to the teens has been a Montbell super stretch #2 rated to 24'F. Using my DM7 and a 2' square of 1/8" evasote for my lower legs and then wearing my MB down inner jacket and pants inside the bag inside my tent, I have been warm through the night at 10,000' in the Sierras in mid October in the teens. I do sleep warmer than most of my hiking friends, but I would say that using a bag rated to 20'F combined with warm clothing worn inside the bag, and, as Roger said "seriously warm head gear" would allow you to get down into the teens at least.
Since you are only planning to be out for two nights, the issue of moisture condensate in your bag will probably not enter the equation. But if you do intend to camp like this more often or for longer periods, maybe it would be a good idea to consider investing either in a warmer bag, warmer ground insulation, warmer outer clothing or a combination of any of the above to make a more appropriate sleeping system. Just remember any of the improvements you make to a cold weather kit will also be usable in warmer situations.
I bring my WM Flight jacket and MB down pants along on trips where it "might" get as cold as 25' or 30'F in combination with my MB SS #5 which is only rated to 40'F. I use my DM7 as the pad of choice. In this way I am going to be comfortable whether it is 40 or 50'F or 25'to 30'F. You can carry a lighter more compressible bag if it is incorporated into a sleep system that provides flexiblity.