SLOWING down the rust monster..........

We used Ospho on my sons Dart to stall the same issues. Cleaned out the rear quarter/trunk drop area as best we could with an air hose. Sprayed Ospho in there until it was dripping out. Pulled the rear seat and rear door panels and did the same thing, until it was dripping out of any gaps and the drain holes. Ospho is a rust convertor, so its supposed to stop the rust.
Thanks all. Can anyone tell me of a way to clean out the lower/rear rockers? I dont remember seeing any plugs up top, but considered drilling one in order to clean out and then spray something inside? I do seem to remember that the bottoms of the rockers had pinch welds that would allow some water to drain- until they get plugged up!