How do you clean/remove rust on the inside of chrome bumper?

i see some are skeptics of the POR, if you put it on clean metal it may peel, and if not cleaned with the proper cleaner it may peel, because cleaner changes the rust to iron oxide, but i have a back and front bumper brace off 74 duster that is used in 5 mph impact, i POR them nearly 3 years ago but did not use them, they are leaning on the side of my garage outside and get rain, snow and evening sun, they are still black with no rust and if you try to get the POR off you have to chisel it off,POR is not made to use like Flex Seal, put it on too thick and it will roll up, but if you spray it on like painting a car it has always worked for me, and my body man of 30 years has been using it, says he has never had a problem with it and no customer complaints,,,meanwhile i will bow out ,i have other fish to fry.