You can tuck it away in the engine bay in an area it's easy to get to but is supported...
or...
You can cut the wires, and elongate them, and then mount the optimizer in the engine bay.
I should prewarn you, tuning with this will take a long time, and is a pain in the ass. Also be careful. You can can make it lean enough that you'll knock, or rich enough that the car won't move. And DO NOT rely on an AF gauge to do the tuning. They are bot reliable, and are pretty much useless. An OBD2 scanner will help a little...
Good luck...