dont forget to pick up a mounting kit and wiring adapter.
i just changed mine out with a kenwood ddx512 (the harness plug was 14.00 at auto zone/just remove the factory brackets and attach them to the new unit ,and yes you will need the trim piece.there will not be a very large gap on the sides/top of unit but it finishes it all off,it is all very easy.the mounting kit gives you the trim ring you will more than likely need to fill the gaps. if i understand it correctly, its the only piece you need out of the whole kit. as for the wiring harness there is only one. you need the 07 and up or 08 and up(cant remember which year they changed the plug).