I agree. The factory left that air space open for a reason. I put rigid foam on top of the ribs and the factory plywood on top of that. I've had motorcycles in there and the foam has not compressed. I also put my rivnuts in the top of the floor ribs - both so I am not bending the floor when the bolts are tightened and so they are above any water that ends up under the floorwhat's everyone's take on floor ventilation, as talked about here?