I have a 2001 Crossroads Prep Series 33. The exterior walls, at the rear slide, are beginning to show stress cracks at each of the four corners of the slide. The stress cracks are on the main exterior wall, not the slide. The stress cracks are extending diagonally from each corner, away from the slide opening. The cracks are about 3 inches, or so, right now. Is there any experience, or are there any suggestions as the best methods and materials to use to repair this? Also, would this suggest any improper use, causing the damage to the exterior wall?