Suggestion : I bought a kit years ago that came with a insertion tool and various sizes of rivet-like studs that are internally threaded.
You drill the appropriate sized hole ( with a drill stop mounted to the bit ), pop these suckers in and you are good to go.
HINT: make very sure you know EXACTLY where to drill the holes !! )

A little history : I got this kit so I could cut a section out of the floor in my Suburban that allows me access to the gas tank fuel pump and level sensor. ( Try dropping a 40 gallon tank ).
I cut the section out with a metal blade jigsaw riding on 2/4 sections so the blade didn't go too deep, replaced what I needed to, then cut a plate that overlapped the hole by 1" on all sides. With the kit, I inserted the studs, then mounted the plate using a rubber gasket.