I have seen fairly late model dodge trucks here with the bed side rotted out and you can see a rope looking piece in there that didn't help the problem
You beat me to that observation, Bill. Same here too on Long Island...many new trucks with wheel opening rot. Looking closely at them I can see no matter how much care the owner does to the truck, that is still rotting from behind the paint and from an inaccessible cavity.
Late mode Dodge rear wheelwells have holes that allow water and debris to be trapped and begin rotting the pinchwelds and metal from the inside. Chevy trucks do the same thing by a similar design. Dodge inner rockers have factory taped over holes that provide access for application of rust prevention products and cavity waxes but I've never seen an owner do it. That is why I do so many rocker replacements. Dodge rockers are triple walled and the center wall completely disintegrates. Frame rot is common, shock mounts rotted off are also. All pinchwleds are prone to failure simply by neglect.
Chevy rear wheewells have plastic plugs which provide rust prevention access but again, no one does it. I rebuilt an '05 GMC last year with 62K miles. It needed full rockers , cab corners, and door bottoms. Cab corners are foam fillled which gets soaking wet. No amount of rust prevention can stop it because it's inaccessible. Corner replacement is inevitable. Chevy rockers are also triple walled and the outer wall is very thin. Repro replacement rockers are 16 gauge and superior to GM rockers.
If people took immediate measures upon purchasing a vehicle, many, but not all corrosion problems can be avoided. Salt and calcium chloride destroys daily drivers and work vehicles. It's still cheaper to fix the rot than spend $40K+ on a replacement truck. Some let the rot progress and repair becomes out of their financial reach.