op wrote:
I check my tire pressure religiously. I am OCD about appearance and up keep of the trailer so everything was well cared for. Its even stored inside so the only time the tires are exposed to the elements are when we are camping.
Most likely someone will be along shortly and tell say you some how abused your tires as tires simply don't just come apart. Victims know better.
Your story is typical of ST tires even when they were all made in the USA so made in china is not the whole story.
You added load E tires I believe for more capacity which comes at 80 psi. Keep them pumped to the max so you can take full advantage of the new tires extra capacity. Derate them with lower pressures and you loose their advantage.