Well I just had my first blowout, 40' Monaco diesel. This was a 275-70-22.5 Hancook that I put on in February 2012. I really thought they would last a little longer than this so I wonder if I should ...
I also tow a race car trailer with a DP and run 100lbs in all 6 tires. It was 95+ around here the last couple weeks and I went up to MD (350 mi) and back in the heat of the day with no problem---I have a 32ft Pace tri axel trailer that is really heavy and have towed it over 100,000mi. Those tires aren't that old.