2004 2500 HD Rotors warping

I have a 2500 HD 2004 6.0 l and the rotors keep warping. I bought it from a dealer with 8100 miles on it last year and I've had them turned already once by a private person. The truck does sit alot without driving so I was wondering is the inactivity or the quality of the rotors on these trucks the real culprit. Any suggestions would be great. The truck currently has 17100 miles on it. The last time I warped it I was triling my snowmobile when I noticed the shudder when I used the break.