Okay, now that I see it, the lower opening could be correct for the access to the backside of the refer in a1963 Sovereign
. PM Fred Caldwell to explain the top opening. He is the world's foremost authority on Vintage Airstreams of that period.
Are you sure the upper vent (Not shown) is for the refer? Is it an oblong rectangular hole or a round hole? Some of these came with a panel ray heater.
Also check and find out when Airstream evolved from Ice Box to Refer. Not sure what came standard in 1963