tire wear

hi there..
I am new to this forum and i have a very important question.
I have a 2001 tahoe lite 17' travel trailer i use it every summer rain or shine or snow if you live here in alberta... anyways this past summer i noticed unusual tire wear on both tires(single axle) both tires were bald on the inside and fine on outside .. unfortunately blew a tire coming back from camping and that was an experience ... what could be the problem and how much could this cost to fix????? thank you in advance for the help...