One thing people may not realize is that the Grande Armée did not use tents on the Russian campaign. As hard as it may be for us to imagine, according to John R. Elting in Swords Around A Throne, Napoleon did not approve of tents. “It is much better for the soldier to bivouac because he can sleep with his feet to the fire, which quickly dries out the ground on which he lies A few boards or a little straw shelter him from the wind…”
“Tents attract the attention of the enemy’s staff and make known your numbers and the position you occupy. But of an army bivouacking in two or three lines, nothing is perceived in the distance except the smoke, which the enemy confounds with the mist of the atmosphere. He cannot count the fires.”
Elting points out that tents also require time to pitch and strike as well as hundreds of additional wagons for transport.
As for what it was like to sleep out in the open, he quotes Elzéar Blaze: “When you are in bivouac in the face of the enemy, everyone goes to bed completely clothed, everyone sleeps, so to speak, with their eyes open…. Sometimes we went a month without taking off our boots…. When the weather is cold, everyone sleeps close to the fire, but you grill one one side and freeze on the other.”