A Black Day for Mayberry - S4-E7
Plot hole: There is no reason for a gold truck from Denver to Fort Knox to be going through Mayberry.
A Black Day for Mayberry - S4-E7
Plot hole: About 2/3 through the show Barney is locked inside the armored car and Gomer puts about a gallon of gas into the gun port onto Barney's shoes. After Gomer is told of his error, Barney stays inside the truck. The fumes would have killed him, not to mention the risk of explosion.
Answer: Those "boxes" are valences that used to be very common, before air conditioning. They allow for windows to be open during rain storms. They permit air circulation, without letting the rain in.