I don't know because in 35 years of trailer towing I've had 1 blow out. Even then I don't think it was a blow out, just a flat that I did not catch in time.
I break all the rules know to mankind with ST tires. I tow the speed limit, and in most of the stats and roads I travel that would be between 70 and 80 MPH. I tow only in the summer so heat is always an issue. Almost all the tires I have had on my trailer were cheap China made tires.
From what I have seen, most people flat out don't know they have a flat tire or even a tire completely gone off of the rim. Seen quite a few trailers towing down the road on 3 tires.
I just don't even worry about it. No problems here.