In Saints Row: The Third (aka Saints Row 3) for the PC, PS3, and Xbox 360, you can add any vehicle in the game to your garage to keep as long as you’d like. There is a catch however.
First, you must obviously steal the car and drive it to any of your current cribs. Which one doesn’t matter, as long as you drive it to your crib, pull it into the garage and exit the vehicle.
Once you exit the vehicle inside of the garage, it is automatically added to your list of vehicles.
However, if you want to keep this car permanently, you need to modify it, even one simple modification. Change the color, add performance, it doesn’t matter what you do just change something.
Once you’ve modified the car, it will stay in your garage even if you take it out and blow it up or drive it off a cliff.