Make sure it isn't a blanket made with polyester - polyester melts and smells nasty! But anything made with wool or 100% cotton should do well, also canvas tarps work good to.Got an old moving blanket? Or small old cloth tarp? Put it over the smoking chamber but not the fire box section. Keep an eye on the blanket to make sure it does not start to smother (aka catch on fire). Add more fuel and open the damper so it builds up more heat.
Seen on pit masters.