Your serial number should identify whether the coach is considered a double or a twin. If you find a "D" in the serial number it is considered a double. If you find a "T" in the serical number it is considered a twin. My Minuet has the same "L" lounge you describe and it is considered a "T" twin.
During the time when your trailer was manufactured, all Airstreams were considered Land Yachts. As an option, it could have been equipped with the International package which would have included upgrades to a number of systems in the coach (the upgrades and contents of the International package varied by year). The International Package's presence is usually identified by a placquard attached to the side of the trailer near the door - - the serial number plate should also be found there as well.
Good luck in resolving the issues with your insurer.
Kevin D. Allen
WBCCI (Lifetime Member)/VAC/Free Wheelers #6359
1964 Overlander International/1999 GMC K2500 Suburban (7400 VORTEC/4.11 Differentials)
1978 Argosy Minuet 6.0 Metre/1975 Cadillac Eldorado Convertible (8.2 Liter V8/2.70 Final Drive)