Thanks for all your comments. It appears there is no good solution to this Airstream self created problem. Using the existing wheels means that I must retain the "C" rating...upgrading to a "D" rated tire could split existing rims due to increased tire pressure. Getting bigger wheels/tires causes a whole new set of problems. First, the brakes on my 23FB are 10" and designed for 14" wheels...increasing rim size changes breaking dynamics. Second, the wheel wells aren't really big enough for 15" rims without modification, which is not only a pain, but can be expensive.
One thing that no one at Airstream tells you when you purchase a 23FB is the wheel size. More importantly to the owner, the ST215/75R/14 has a maximum speed rating of 65 MPH...they don't mention this either. If you exceed that speed for any length of time (like with interstate driving), you will lose some control over the trailer and damage the tires due to buildup of excessive heat. I know as I had a series of catastrophic blowouts that totaled a 2003 Safari.
With all that said, I don't want to experiment with any "homebrew" modifications on my relatively new 23FB ($60 grand investment). Aside from it not being recommended by Airstream, I'm frankly not sure what new problems this professionally untested fix introduces into the mix. It might even make the trailer un-insurable. All I want is a reliable tire of the size recommended by Airstream. I can't understand why this is so hard...seems you have to be a rocket scientist to figure out what's what with the tire industry. My conclusion is that Airstream doesn't care about the safety of their trailers after they leave the lot. So...bottom line, at this moment, the best bet for me seems to be the Maxxis 8008 ST215/75R/14s.
Is there evidence to suggest the rims will not hold the extra tire pressure? I was set on trying the kumho's because of the great reviews I've seen.