https://images.duckduckgo.com/iu/?u=...omrear.jpg&f=1
^^That is a Prius
You could start by finding a picture of the 2016 undercarriage. I didn't try very hard. I did see a comparison of a 2011 and 2016 Prius and the bellypanning was much improved.
But say you wanted to add one anyway. Right?
You can put it on a lift and use a plumb bob to transfer the locations of mounting points to the floor. One big piece would be optimal, but how do you get it under the car?
Coroplast is not fit for purpose and fiberglass is noxious and tedious. I suggest composite cladding; brand names include Polymetal, Maxmetal or Alumapanel. Stiff as 5/8" plywood at 1/10th the weight and twice the price (worth it because it is
pre-finished). I've worked with samples:
Mostly it's used for signage. And wings on dirt-track race cars.