I finally thought it was high time to get my bumpers out of the weather and starting cleaning them up. I cleaned the bumpers and then started the three step POR 15 method of fixing the inside bumper rust. That area is not chromed, so it is always rusty back there. First, I got my hand drill and a wire wheel and knocked the loose active rust off. Then, I used Marine Clean to clean the area. After washing the Marine Clean off, I used Metal Prep, which acts as a rust neutralizer and a pre primer. Then I applied the POR 15 gloss black. After two hours, I applied a second coat. On the first bumper I did, the rear, I forgot to put masking tape over the bolt holes. As a result, paint ran through the hole and ran on the chrome side of the bumper. Bummer! This paint is so tough, you can't take it off, even after just 30 minutes. You are supposed to top coat it if it will get any sunlight. I don't think the inside of the bumper gets much sunlight, but I could paint it will Rustoleum silver if necessary. I even did the same process on the insides of my bumper brackets. I'm thinking of also doing the insides of the doors and any other hidden place that might rust. I think the chrome side of my bumpers are good enough to clean up just with using some chrome polish and steel wool 0000 fine on them. In fact, the rear bumper was purchased 40 years NOS for about $75. I was covered with hardened cosmolene. I had to use paint stipper and spatulas to get it off. I have two front bumpers and three rear bumpers, so I chose the best of each for my restoration. I wonder what the going price is today for getting a pair of bumpers rechromed?