I know it's not exactly a source, but I was playing the Black Ice mod for Hearts of Iron 3, and one of the techs (battlefield modified armor) stated that tank crews would scavenge scrap metal and armor from enemy vehicles and attach it to their own tanks as a sort of makeshift armor. Are there any accounts of this actually happening?
Followup: If they did, is there any evidence that it worked? And if it did, why weren't the tanks designed that way in the first place? (Tradeoff with fuel consumption?)