HELLO DAVE,YOUR RUST PROBLEM SEAMS VERY ADVANCED,AND I THINK USING A RUBBERIZED UNDERCOATING WILL ONLY FURTHER ENTRAP MOISTURE.THAT ALSO GOES FOR THE PAINT OVER TREATMENT THAT YOU ARE APPLYING.I AGGREE THAT CUTTING OUT RUST AND PUTTING IN SOLID IS THE BEST WAY TO GO.MY VIEWS ON RUST IS TO STOP IT BEFORE IT STARTS.AS FAR AS STAINING RUGS GOES WITH THE INSULATED FLOOR MATS UNDER THE RUGS IT WON,T HAPPEN.YOU MUST HAVE A MOISTURE TRACK IN THE AREAS IN QUESTION,THESE HAVE TO BE STOPPED AND MOISTURE DRAINAGE RESTORED.I LIKE THE 3/M BLACK BODY SILICONE EASY TO WORK WITH AND CAN BE STUFFED INTO A LEAK AREA.THE LUBRIPLATE CHAIN OILS I USE ARE ONLY 5 TO 6 BUCKS A CAN AND I PICK THEM UP AT A BEARING DISTRIBUTOR SUPPLY HOUSE.CHEAPER BY A 6 PACK CASE.HOPE THIS HELPS,BEEN THERE DONE THAT.PETE