WZ,
A secondary floor is used in vehicles where there is no actual floor such as a coupe. A secondary floor is generally needed in a roadster, lakester or streamliner where there is nothing below the driver's feet but the belly pan. The secondary floor will keep the driver's feet inside the car in the event of the loss of a belly pan. The flooring can be made of expanded metal, aluminum, etc.
In your case, the current floor boards will be sufficient to meet the the requirements.
Dan