Help with interior

The plates are a good idea , but, there not a mandotory item to have.

What you can do is make a steel square approx. 3 X 3 or 4 X 4 inchs to place under the car so the floor doesn't bend or kink when driving or braking becomes spirted. The plate should be as thick as you can get it for stiffness.
Then add a lock washer and lock tight to keep it from ever moving anywhere.