I hate with passion the unibody concept. With the rear quarter panels (as you called them) welded to the structure damage to them is a challenge to repair. Just imagine what it will take to replace that panel. Lots of cutting, some temporary reinforcing the unibody to stay within dimension specs, removal of glass and upholstery, and gross welding all around. Remember the existing piece is spot welded by robots. An then the dipping coatings thar that reached every inaccessib;e nook and crany will be vaporzed by the welding being humanly possible way to reapply it. This is a formula for rust in the not very distant future.