When looking at an RV, be sure to look carefully around the frame of the slide-out. Some manufacturers have issues with the structural integrity of the slide frame. Look carefully to see if any body repairs have been made at the corners of the slide frame. Most likely, if there is any damage you will see it at the lower corners of the slide frame. When the slide is fully extended, there is a lot of torque on the side wall.
To fully repair damage would require extensive work and cost.