Me.
You can get them in 80 and 85 series - so try to match what you've got already. My guess is that they are taller than average spec due to tread depth.
I replaced factory tires with 637s as soon as I bought the trailer. I can tell you that the weight difference was 35lb (factory tire) to 61 lbs (Sailun).
Yes, they are from China.
Yes, they have a very good reputation.
They're imported by TBC Corp who owns a bunch of American tire stores, so they are backed by a real company here in the USA.
I'd buy them again in a heartbeat.