heh, yeah POR-15 is some serious stuff, i'de use rubberized undercoat or truck bed liner first, but if your serious about wanting it PERMANENT, go for it, i've seen it used in applications where it was used as paint, and it wasn't bad, only problem is lack of colors, and if you ever want to paint it again, either rough it up during the cure time, or grab some COARSE sandpaper, and get ready to tire yourself out. really its not practical to sand after curing.
the thing to remember with POR-15 is its pretty permanent.