All good replies. Sounds like a high load index passenger car/light truck tire may be the best option absent a dedicated trailer tire. I agree that the trailer tires have a different construction, one being stiffer sidewalls. The stiffer sidewall prevents swaying. My concern with bias ply tires is that they would wear faster and also be prone to swaying.

Having said that, I must admit that even at my advanced age, I never had the opportunity to use bias ply tires. As I became of auto age, radial tires were plentiful and inexpensive (relatively).

Ralf from Alfred Spindelberger mentioned that they ship Cobra trailers with "C" rated (Cargo) tires. Cargo tires are constructed with stiffer sidewalls and are overall more heavy duty. That's the type of tire Mike mentioned. His link is to a local Florida chain, but I was able to find a store in the Salt Lake City area where I live that advertises the same tire. We shall see.

David