I am a new member but have been lurking for about 6 months so.....at the risk of being kicked out, I have a tire question. I purchased a new to me 2009 31 foot Keystone Hornet TT in September 2013...
If the tires show no signs of degradation I would continue to use them until the first signs of a problem. Inspect them religiously including the tread area for any signs of cracking and monitor air pressure at each use. I personally would not replace them with anything but Maxxis brand M8008 radials if you continue to use ST tires, preferably in the E range tires.