Headunit kind of is what it is, if the car doesn't have a spot to put screws in to the spots on the side of the headunit, then you're either SOL, or going to have to get creative with fiberglass, plexiglass, wood or sheet metal to put a panel in there you can put said screws through. For everything in your trunk, you put a big ass heavy piece of wood that barely fits in there, put the carpet over that and then screw everything down to that. You'll need brackets for the woofer. If you're feeling really ambitious you can even screw that piece of wood down to the metal in the trunk.