Auto body repair & detailing: rusting from within sliding door, kill rust, ford repair


Question
I have a windstar 2000 which just starting showing signs of rusting from within the sliding door on one side. It show up as two 3/4 inch wide and about 4 inches lone on the lower edge of the outside of the door.  Of course it is out of FORD's warranty (5 yrs-unlimited miles).  It looks like that door did not get the corrison coating on the inside.  My question is can I take the inside panel off and coat the inside with a 'kill rust' or its equivalent, and fix where the rust has gone through the door?  Another question is how do I take the inside panel off to do this to the door?
I talk to Ford Corp. and they would only cover about $800 of the cost at a Ford repair shop which estimated a cost of over $2000 (door replacement and paint).  That is more than I want to put out for a car that old.

Answer
YES YOU CAN USE A RUST KILL OR REMOVER.IT IS BASICALLY JUST
A HEAVY CITRIC ACID.MAKE SURE YOU RINSE IT OUT WITH CLEAN
WATER AFTER AND ITS COMPLETELY DRY BEFORE APPLICATION OF ANY
INHIBITORS OR UNDERCOATING.
THE DOORS INTERIOR PANEL IS HELD ON WITH PLASTIC SNAP CLIPS
AND SOME SCREWS , TORQUE OR PHILLIPS.