I did not read through the comments but here is what I know. On a trailer that is going to sit buy bias ply tires. Age and sitting does not affect them much but they don’t last as long as radials. My cattle trailer tires are 11 years old and it gets used two or three times a year.
The other trailers are used almost every week so those get radials.
The other trailers are used almost every week so those get radials.