My set of Goodyear Marathon load range C tires that were dated 2002 (2003 model trailer built in Oct 2002) finally got replaced this year after about 11,000 miles on them (had a blow out shredding of one that previously was patched for two nail punctures) We got the trailer new in late 2003 so call it 12 years service.
They were made in Canada. No idea if that makes any difference to anything. Kept mostly out of the sun and not much mileage per year is probably the real story on that.
Now have a new set of Carlisle Trail RH Ds. I expect they will last us out for this trailer.