I present to you a 1988 Fiero Notchback.
My intention for this is for it to be played with by my nephew, so I made the walls rather thick at 2.7mm. This may affect resizing efforts below 5 inches lengthwise.
My source model included the interior, but I have removed all of that for ease of slicing and printing. Using Meshmixer and 3DBuilder I was able to accomplish this.
30% Should be more than adequate
I made this model 2.7mm thick so that it would withstand a little kid playing with it.
I sincerely love Fiero's and it took a lot of time to properly prepare this model. I hope you enjoy it as much as I.