All heat and a/c air handling in Airstreams are handled by flex tubing- normally a silver color and made from fabric wrapped spring wire. The fewer twists, and excess length used, the better the air flow and velocity.
2000 390 Landyacht XL
1989 29' Excella
WBCCI #6673 jerry Hodge
Have no intention of arriving at the grave safely, but rather to skid in sideways, chocolate in one hand,throttle in the other, totally worn out and screaming
"WOO HOO, WHAT A RIDE!"