Ohhh dangerous!
The whole rocker (sill section) comprises of an inner, middle and outer, all of which contribute to the strength of the car, ties the A and B pillars together etc. IE it is a structural component
You can get "covers" for the outer panel. I have seen them in black fibreglass for the CSL look and polished stainless. All to replace the chrome strip that is standard.
What ever you do end up using use plenty of anti rust wax as water will inevitably get in and start the rot process all over agaim
DO NOT use covers to hide rot, your just kidding yourself. If I saw a car for sale with them on I would be very suspicious as to what they were hiding.
Sorry a bit of a sore point with me...
Malc