On the driver's side, adjacent to the electrical and below the galley plumbing, I used 404 steel sheet. I made a wooden box and attached the steel sheet with adhesive and screws into the box. This is the same plate that is used in garbage trucks and process chutes. I have full confidence that a spinning radial belt is not going to get through it, quickly.
On the passenger's side, I reinforced the plastic wheel well with conventional sheet tin. I attached it in two directions, hoping that the tire belt won't tear into the frame quickly. There is at least two inches of clearance before it can hit the wheel well frame or the plywood that encases the well.