When I pulled the carpet from my car I had the same problem, so I made a set of lightweight floorboards. I cut a piece of black foam-core poster board to the same shape as my passenger floor mat. This was bent/creased to match the floor, then I put two layers of fiberglass on each side to hold that shape and make it sturdy. I finished the top by spraying it with truck bedliner paint. I cut a few pieces of PVC pipe to even out the car floor, then secured it with 4 bolts. Looks race car proper and works great, even on rainy track days.
