I'm sure I've seen that before somewhere, but this truck isn't mine so I'm not keen on slicing it up. it lives in georgia and so I cleaned up and treated the inside and then sprayed flex seal on the inside and deemed it good enough to outlive the truck. up north and with my own truck, I'd probably do more.
But the rust is inside the seam, so there's a limit on what can be done. you'll never get it all without tearing apart all the panels (and honestly that would likely do more harm than good)