Bart - he's refering to the molding at the bottom of the quarters as 'rockers', the rocker patch panels available are the same shape and can be used back to the start of the wheel opening, which is the real problem area
the panel truck lower half construction is identical to the burb, and the primary reason they all get rotten is the total lack of finish on the inside of the double wall panels, doesn't require any leaks .... over time simple condensation results in surface rust that flakes off and collects at the pinch weld, slowly building up and remaining wet by trapping the condensation ... the only way to stop that is to finish the insides of those panels or [what I'm doing] leave the bottom open between the panels so the grit doesn't have a place to get trapped and build up
note that you never see a fleetside bed with that kind of rot, only because the fleet doesn't have the inner panel ... OTOH, it took many years of all weather driving for those quarters to rot, and it's unlikely any of us will be using the rebuilt panel/burb as full time daily drivers [except me

]
Bill