Fresh Water Tank on our 6-month old 3585 Bighorn has developed a crack on the bottom of the tank, see attached photo. Failure occurred on first water fill following three months of storage during which time tank was empty. Outside Temperature was above freezing at time of tank fill/rupture. My best estimate on when complete failure set in was approximately 5-hours after tank was filled. Has anyone experienced anything similar? Heartland has requested dealer send photo of damage before they authorize repair under warranty.