I have a 1996 Discovery 300TDi. I'm replacing the rear floor panel. While doing so, I took a look at the rear wheel arches (the things that protrude into the rear of the vehicle, not the little bit that runs along the door edge). The offside one looks as though it's shortly going to resemble a swiss cheese, it's bubbling that much rust. How easy are these panels to take out and replace, and where can one get instructions on how to do it?