I have furring strips under my plywood, but I used liquid nails to attach both those to the metal floor and the plywood to them. I used tek screws to hold everything in place while the glue set and recommend them for any application going into sheet metal, but the construction adhesive is doing the lion's share of the work and it keeps everything feeling really solid. I pre-drilled all my holes, but that was just to keep production times higher. I had a corded drill and one cordless. Making the cordless self drill all the holes would have run the battery down too quick and a single speed corded drill is a pain for driving screws.