I've heard of and seen them, but don't know the tire size. However, the Condor was an R-Vision brand name, not Airstream. All the Airstream coaches were called Land Yachts and they ranged in size frm 26' to 39' in 2003.
2003 Ford F53 Motorhome chassis came with 19.5" wheels on the 18,000, 20,500 and 22,000 lb GVWR versions and (according to the F53 Fleet Guide manual) the size was 245/70R19.5. The smaller 15,700 lb GVWR chassis had 225/70Rx10.5F size. The latter is a oddball size designation that is usually seen only in offroad or other specialty tires, but I guess Ford used it too.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL