Drill for screws on opposing sides and pull it down in place (a little at a time) with truss head screws and nuts. I would recommend you apply a slow curing sealant between the "hump" and the existing floor.
after cutting and "adjusting" the floor, i used #10 stainless machine screws and flanged counter sunk washers with flanged nuts on the underside. to seal it i went with sikaflex 221 because i had some. i'm sure that 3M sells something dreadfully expensive that may be more appropriate.
i thought the flange washers and nuts gave a little more area to spread the load and looked better than screws or rivets popped thru, and i guess you could take it back apart if need be. i did use a heat gun for some of the problem areas, but all in all it went together fairly easily and it's totally hidden under the carpet. it was about 60 bucks all said with the hardware and sealant.
