Out of all the members of RV.Net, you would be the one with the best skills of getting this done!
From what I hear, the factory installed a thick plastic under the RV and tanks, with insulation in between the floor and sub-floor plastic.
Think of those 'for sale' or Garage sale signs that are about 1/4" thick with ribbed plastic. A sheet of that stuff 102" wide and long as the RV. Of course cut outs for the springs, and such. It is attached to the frame and sidewalls. Just don't apply 2" long #10 screws into the grey and black tanks! LOL.
Good luck,
Fred.
