Shuttle Bus Floor Reno

[travelbus3]

Hi there! We have a 2006 Ford E350 Shuttle bus we are in the process of converting. We are replacing the floor completely. In removing the old plywood we noticed that part but not all of the underbelly is open to the outdoors beneath the wood, some areas have thin sheet metal. We are considering welding more sheet metal to these open areas, creating a full thin metal underbelly below our new plywood.
Wondering about anyone's experience/thoughts on this idea or if there is any benefit to keeping it as just the treated plywood.

Thanks for your help!!