The correct number turns out to be National 412920. Airstream's number is 630370-100 - but they don't offer any cross-reference - and the mother ship (Jackson Center) no longer ships parts. All they do is refer you to the nearest AS dealer. Strange enough, my local parts shop was able to get the seals - but they had to call on three other regional shops to come up with four seals! It seems like each shop only had one seal apiece. Further, with respect to the mother ship, the last set of seals they shipped to me had both CR and National seals in the set - and the part number on the National seals was the "generic" 412920. The Airstream part number was nowhere to be found. It makes me think "customer service" is failing somewhat. Oh, for the record, I paid $19.00 each for the seals.
2003 GMC 3500 D/A, CC, LB, 4x4 and 2000 Airstream Excella 30. WBCCI 7074