The builder of my -6 added some angles to the stringers, and screwed floor plates to them on the inside, making a flat floor in front of the pilot and passenger. The same screws with larger washers under the heads hold down a piece of carpet on each side. You lose about 1/2" of height from the space between the floor and the panel (which you'll never miss), you get a flat floor, and you'll never be loading your outside skin.
During one of my annual inspections I cut pieces of sound-deadening foam and placed it in the bays below the screwed-in panel. That cut the noise even further, but I will probably replace it with some glass-fiber-based insulation instead to better guard against heat from the nearby exhaust at the front.