I read a book on these operations a while back. Many of the aircraft are very well maintained but also very old, having gone from USAF to Air National Guard before being given to the forestry service or air bomber operators for a token amount. I think theres even a C87 ( cargo B24) still in operation somewhere, or was until recently. These planes do short hard sorties at low altitudes, and thats hard work for any airframe, espescially in the turbulent conditions around summer forest fires. Those guys deserve more recognition. They have an incredible level of professionalism.