Aunt Bee's Brief Encounter - S2-E9
Other mistake: Mr. Wheeler's license plate number is 'DC 269' which has been seen in earlier episodes. Then at the end, when the locks-keys man pulls his truck into the driveway, it has plate number 'VT 772' also seen in episode 2x5, when the pretty woman drives into town.
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.