Hi Norman
Yes, you are correct, they do corrode as I recently discovered on my own car.
The trick is to replace them with copper or Kunifer. (available on eBay and Amazon or from your local Wilco’s.) That way you can still keep them inside the floor stiffeners and they won’t rust and they will be protected from damage. Remember how low our cars are. Mine had a rubber ‘bung’ pushed in at either end, this had stopped any rattling but also stopped moisture from draining out – hence the rust.
Cheers
Paul
Paul Barnard