I love that stuff, check out por15.com they can tell you what is for what,
for your situation, it depends on the metal, is your trunk in good shape, or is it swiss cheese? If its pretty descent, the metal cleaner may not be needed, just clean the trunk well, and wirebrush it. it gives POR15 somthing to stick to. you can use metal etch if you wish, but like i said, it depends on the condition of the metal. POR15 chassis black is wonderfull too, I combine it with their fiberous patch to cover some holes in my floor and after applying the por15 it is as hard as steel.
wear gloves, if you get it on your skin ,it does not come off,. (although while fresh fingernail polish remover tends to break it down) but if it dries, the only thing that will take it off is wear and time.