If I understand your question, you repainted your camper and left the z raw aluminum?
If yes, you'll feel the paint line. I usually polish the Z before painting. With that said, if you sanded along a taped line and primed (primer for nonferrous metal) before painting you should be fine. Auto paint is very, very tough, oil enamel is very durable, latex house paint is not ideal for anything but the short term.