I had 8 floor "D" rings installed by the factory. All 8 used 3 inch self tapping screws that were aligned to tap through the frame rails. I added 4 (2 center D rings for each side) From what I can tell, the floor is 3/4 inch plywood with the rubber tread plate floor on the inside and the mesh on the outside. Mine were counter sunk, so I flipped the new D rings over for the pattern. Then I used a 3in hole saw to start the process for depth and a chisel to remove the rubber and plywood to counter sink the new rings. I used the same 3 inch self tappers to hit the Frame. If your mounts are Not going to align with the frame, I suggest you use a plate on the bottom and bolts with lock washers or self locking nuts. Your garage should be pretty easy to view with no chloraplast liner. (Unless you are mounting above the gas tanks)
for a tool box, it would depend on where you install it and the width of the box. Probably going to require a small steal plate to insure you don't pull through the wood during travel.