Cracked the bed of my truck

Thanks for all the responses. I agree with all of you that it is metal fatigue from the bed flexing. I know with my 06 the bed definitely settled closer to the frame with the camper on, but I haven't seen that with the 11. Probably just the difference in visual cues, my airbags were/are different for each of the trucks. I do have a rubber mat in the bed but it could be that it is wearing out a bit. I've had the mat since I bought my first camper way back when. I was thinking along the same lines with the plywood being able to spread the load out a bit more. I hadn't thought about checking the level of that seam. I'll do that tonight if I get the time.