From the first time you play the game you can customize every slot on a battle-car with an 'octane' body apart from the 'topper', so keep playing matches regardless of whether you win or lose until you unlock a topper.
Then from the main menu go into 'garage' and customize each of the following slots to unlock the trophy making sure to use the body called 'octane'.
Decal
Paint
Wheels
Rocket Trail
Topper
Antenna