Passenger seat is for extra tires? She gets a taxi? Just kidding, GTS fits a rear wheel right on top of the spare tire, Intake manifold, 4 brake rotors, airbox, coil springs, 3 rear axles, stock headers and front bends with flex, front & rear wheel with tires, car cover and many other Viper stock parts fit into my modified '01 GTS for the drive from Ohio to BC when I bought it. I didn't have room for the Nitrous bottle (which I never received) and the other 2 tires and wheels (which were shipped to me a couple months later).
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That's the reason I bought ONLY a GTS. It even fits the wife's 2 suitcases and shoe bags for a 2 week trip!!! We even have all the hatch room for coming home with souveneirs.
Ted