You didn't mention what could be some important issues.
How old are the tires? If they are more than 5 - 6 years old it's time to replace them all no matter how much tire tread is left. Tires deteriorate from ozone and sun exposure weakening them. They also deteriorate when left in one position for a long time as the oils in the rubber leach out from the portion contacting the ground leaving a hard brittle section of tire that takes a "set" where it is compressed against the ground.
What is the weight of the rig, real weight not a guesstimate? Are the tires overloaded when you are traveling? You need to run the rig over a scale while loaded as if going out and compare what the axles are supporting to the sidewall figures indicating what the tires are rated to support. If the rig weighs more than the tires are built for, you will have more failures until you lighten the rig or install better tires.
Do you check the pressure each day before moving? Inflated properly for the load the tires will run cooler and last longer.
Lastly never replace one tire on an axle with another tire of a different rating or size. Replace both tires on the same axle with tires that are the same. Replacing them all around is best when it's time to do so. Don't forget the spare especially if it is outside and exposed to the elements. If you are replacing the mounted tires with something different (size or weight rating) change the spare too.
Mike Nancy and the fuzzies
Fulltiming since June 2004
Volvo 660 MH tow vehicle
2005 MS 38RL
2007 Saturn Ion "toad"
2010 Gold Wing "piggyback"