That is a vent to allow for air convection so your fridge can cool. It's factory, not aftermarket. Your fridge (if original) has no compressor. It is of the ammonia-absorption type. You can learn all about how they work here:
AIR 2053 Current: 2006 Born Free 32 RQ Kodiak Chassis, & 1995 Coachmen B-van
Former Airstreams: 1953 Flying Cloud, 1957 Overlander, 1961 Bambi, 1970 Safari Special, 1978 Argosy Minuet, 1985 325 Moho, 1994 Limited 34' Two-door, 1994 B190 "B-Van"