I purchased a new Mazda Pickup truck 2 years ago, and put a factory made aluminum Lumber rack on the truck. Last year I started to see a crack occurring in the bed of the truck, near the front upper corner of the panel. As I examined the truck, I found that the outside drivers side panel had not been welded were it meets the outside front panel of the truck bed. You can literally move the side panel around by hand. I checked the other side of the truck and it was welded there and secure, I checked my 1 year newer Ranger (they are practically the same truck) and it was welded there also. So even though I knew there was a possiblity that weight on the Lumber rack could have been a factor (although I don't carry alot of weight on it), it was quite obvious that the missing welds were to blame, and the dealer agreed with me. But when the dealer called Mazda USA they refused to repair the bed, saying that if you put a lumber rack on their pickup truck you void the warranty on the Bed!!!
I couldn't believe it, I talked to Mazda supervisors, at first they tried to say the dealer said it should not be under warranty, but after doing a conference call with the dealer and he again agreed that the missing welds were to blame, the Mazda supervisor would not back down and just keep restating their policy.
I think that it is amazing that they can sell you a truck designed to hold a lumber rack (it has the holes in the bed top for a lumber rack to fit into) not say anything about no warranty on the truck if you put on a rack, and not stand behind their truck when it is obviously missing a required weld.