I do not recommend that other RV owners stretch their tire life for 14 years as I did. My situation is the exception, not the rule.
1) Our rig is stored indoors under climate controlled conditions, when not in use.
2) The tires get minimal sun exposure.
3) The load on the tires is far below the tire max rating.
4) The absence of sidewall and between-thread cracking, encouraged me to keep the tires so long.
5) None of the tires were punctured/repaired, or otherwise damaged in any way.
6) Given only 40,000 miles of use, there was still a very generous amount of remaining thread.
I found it interesting that our 2007 Ford E350 chassis that was built in 04/2007, the date code on its original tires was 5006 meaning the 50th week of 2006. So the actual age of my tires was 5 months older yet. When I bought my replacement tires in 2021, I managed to find 6 identical dated tires with 2 month old date codes when I bought them. I feel I got lucky with that.