I've been doing some experimenting on different surfaces and finding the following, especially since I use a lot of different rattle cans on different stuff. The hammered is just for appearance. Its not flexible at all. The bedliner is slightly different but I've found over winter that it does not expand or contract. I've had a new, super clean battery box of thin metal that would expand and contract and with the temp changes the bedliner just flaked off. Regular mopar paint did well however. On a side note, for black I'm finding the plastikote is durable as all get out. Another option also though, and it only comes in gloss is sprayable epoxy appliance paint. Takes forever to dry but its also damn near indestructable. Not sure about how it works with the flexing but having used it on washers and dryers in the past which shake, rattle and move I've never had it flake at all. So I'd suggest the appliance epoxy or plastikote. Especially when you have issues with temperature changes and flexing.