When our original Marathons failed in 2008, the Goodyear Tire Store in Cortez said that he couldn't make an adjustment on them and suggested that I take the tires back to the Airstream dealer to see if they could do anything. The tire that blew out completely disintegrated, and all that was left was the bead and a little bit of the sidewalls. The rest of the tire was back in northern Arizona scattered in pieces along the highway. In any case, if the alternative had been to put two new Marathons on, I wouldn't have taken them. Once was enough.
I have since switched to 16-inch wheels and Michelin XPS Ribs (225/75x16), and they fit in the wheel wells fine. Both tires had to be deflated to get them over the hub, but that was no different from the OEM 15-inch wheels and tires.
If interested, see details and photos on this link:
I am just glad to get this problem behind us, so we can get back on the road with no worries about blowouts.