Once we put our kneejerk 20th century reactions away, its a great way to sleep campaign. The steps are really the same as sleeping alone - only doubled. If you have straw, leaves or any other insulation, put the gum on that first. Now, you and your pard lay down. Use your knapsacks as pillows and follow all the good advice in Mr Heath's piece above.
Moderns are too phobic to do that, so most modern pards sleep back to back or on their backs.
Obviously, they got tight.