As far as rattle can bedliner
I would stick with Rust-Oleum. I have seen post were the Duplicolor liner has faded badly. I think there other types of spray-paint are more color safe. People tend to really like there wheel paint at least.
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I bedlined my grill with rustoleum rattle can and it came out really nice and even. It's texture is about like 100 grit sand paper. That can make washing it with a towel or sponge next to impossible, and basically means you have to pressure wash it.
I bedlined my tub with U-Pol Raptor. I would think that stuff would be ideal for your bumper because it is bumpy but smooth and easy to clean. You need an air compressor though to spray it. It comes in a kit with the gun for about $125 for a gallon.
As for the prep I would sand it down just a bit. Its probably not totally necessary, but I would making sure there is no rust for sure. Then I would put on some gloves (to keep your hand oils off) and wipe it down with Acetone, MEK or Mineral Spirits. I think spray bedliner doesn't ask for primer on the can. I would still put down one
solid coat of self-etching primer (rustoleum it comes in olive green). It's especially made for helping paint stick to metal. After that you can spray it with what ever you want and your going to have the best chance of it not peeling.