A friend of the family owns a local Line X shop. He was actually the first one that turned me onto POR because of the restorations he's completed. He POR'd his truck and Line X'd over it many years ago...he recommended it for our climate. If you are not concerned with rust, then prime it. It will stick regardless if it is prepped correctly. If you are concerned with rust, then you want the por down, period. The Line X will not stop rust regardless of what they try to sell you on. Trust me. If any rust starts, it's going to come right through the Line X, faster than the paint. A trailer manufacturer here set up a deal with a RhinoLine dealer and sprayed all the trailers, flats, enclosed, etc. in various places with Rhino on bare metal. All of the them are chipping like mad and rusting crazy, not from rock chips, the stuff is just falling off. Now there is crap loads of warranty claims and he his having them blasted, then POR'd and re-lined. From what I've observed out here (again, could be different in you climate), I def. not go bare metal. The POR is a small investment for a big return.