Increasing Payload by swapping out my Truck Bed

I would be concerned about the stress applied to the bed hauling a camper. My 06 F350 Dually has stress cracks around the bolts that hold the bed to the frame. The rear opening has spread enough that the tail gate won't latch without using a ratchet strap to pull it together. The only significant weight this rig has hauled is the camper.

Chuck