The Yokohama RY215s are nice because they are high quality light truck tires available in the size that Airstream used originally - 7.00 x 15.
However, they are a bit pricey, and if you need a replacement, your tire store will need to order them.
I went with Yokohama Geolander HT-S LT215/75/15. Load Range C, but more than adequate for the 6200 lb GVWR of the Overlander. We're very pleased; much better than the Duro STs we had before.
Any tire shop would have a P215/75/15 tire available if I needed an emergency replacement.