While you are checking the door sills for rust, remember to check out the metal under the rubber seal going around the rear hatch door. I entered my car this afternoon to be greeted by a nasty smell. Turns out to be that the rear rubber seal is leaking water, which got beneath the carpet/foam which covers the battery area. Quite a bit of mildew. When I pulled the rubber off I did notice a small bit of corrosion. Hope someone catches the same thing before it gets too rusty.

 

While you're in the neighborhood, check the hinges at the top of the hatch as well. My mechanic gave me a heads up that he had to replace the hinges on an R50 that had rusted, making opening and closing the boot difficult. Access was a pain because the car didn't have a sunroof so the headliner had to be removed. His suggestion was to spray a bit of WD 40 into the hinge area and exercise the hatch up and down a few times to distribute it. Drying the area after washing/rain might be a good idea as well.