If it is above the frame, then there is nothing above it but the floor. Push up on it, do you immediately feel the wood floor? If so, cut it out of the way, make a sheet metal repair, and spray with auto undercoating. Don't use too long of a screw to fasten the sheet metal repair to the underside.
Now, on my Work and play, I mounted tie downs. I laid them out, marked, and then used a hole saw, but didn't drill all the way through the floor. Just enough, took a chisel, removed the flooring, enough so the tie down would lay flat. Drilled through the floor for the bolts, and installed them. The bottom of my floor was also covered in some black something, but more like painted on. After I had all the bolts in, I sprayed with auto undercoating.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT