I have experienced that the mil spec ponchos will leak when pressure is applied to them (i.e. at contact points such as the elbows). I carried a GI poncho, poncho liner and a GI casualty blanket while on missions requiring less personal gear than mission essential gear. I used the casualty blanket as a drop cloth, the liner as a blanket and the poncho as a shelter. The only failing part was the poncho. I have since added another casualty blanket as the shelter as well as a cheap painter's tarp. As I always learned "Pack Light Freeze at Night"