I've seen the car. It'* starting to get to the point that I'd call it 'extensive'. Especially in the drip channel along the rear quarters below the windows. In the pics I posted in Your Ride of the car, you can actually see the rust stains on the back of the car where it drips off.
At this point, the best attack would probably be to strip those areas, use a rust treatment/converter, prime, then paint. Of course, use body filler if the rust removal leaves voids.