This account from Albrecht Adam describes some of the conditions faced on the march.
The Viceroy of Italy’s Camp, Wielke-Solezniki
“On the 8th we were hit by such a terrible storm that the Viceroy [Prince Eugène de Beauharnais] and his entire staff were obliged to call a halt to their march along the main road even though they were but three miles from Imperial Headquarters. They did this in an attempt to escape the torrential rain. Horses could make no further progress and anyone attempting to ride soon ground to a halt. Eventually, the march was resumed and we arrived at Headquarters soaked to the skin and absolutely exhausted. Fortunately, a beautiful summer’s evening gave us respite and this probably persuaded the Viceroy to sleep beneath the stars rather than risk a night in a dirty house prey to vermin.”
“One of the Prince’s aides-de-camp, General Triaire, lies next to him on a simple wooden bed with a mattress of straw. A soldier from the Guards of Honour stands sentinel next to the fire.”
Napoleon’s Army in Russia: The Illustrated Memoirs of Albrecht Adam, 1812; Edited by Jonathan North