Everything I have read 6 years is the max. I would guess some stretch it out longer, I don't. I don't put enough miles on to wear them out, but six years is my max on the fifth wheel.
As far as the Sailun's go , great choice over the Goodyears. My second set of tires on my fifth wheel were the Goodyear G614's , about the only game in town at the time. IMO an overrated ,overpriced tire. It was nice to see the Sailun's come along when it was time to replace the Goodyears. The Goodyears are even more outrageous in price now then when I bought them. As I have said the Sailun Terramax is going on my truck when the time comes , as well as on my fifth again .