just stick it in left well well of the trunk, that's the easiest

 

Electrically.... anywhere it fits is where it goes. There is no advantage or disadvantage in any location, just make sure it's near a side and secure it well.
Mechanically ( performance-wise).... the further back it is the better the weight distribution. Also the right side rear would work the best if that's your reason for doing it.

 

thank you....