This is one of the sections that I welded up due to cracking. I did drive around with this weld exposed for a while so when I prepped the bed I made sure to grab a wire brush and give it a good scrub. The wire brush also came in handy in some of the corners.
Don't forget the tailgate of course. Just remove it and strip the hardware out of it on both ends. It's pretty easy. Sand all around the unit and enjoy standing up straight for once. I swear you will be bent over the whole time sanding the bed and spraying the darn thing! Make sure and stretch out each time you begin to work on your truck because it will put the hurt on your back.