Sounds like You may be overloaded!
We had a Brand New 37 Foot Fifth Wheel Toy Hauler back in 2000 that chewed through the Front Tires at an alarming rate. We suspected a bent Axle.
It turned out that All of the suspension components "except the Axles "were the problem !
Springs Shackles,Bolts,Bushings and whatever that Y shaped device is called were just too flimsy ,Even the Spring Hangers were too light for the intended use!
Once We replaced all the Small Stuff and started to Load and weigh properly the Tire problem went away!
We also upgraded to better Tires as the Originals were pretty poor!