Well I did this back in the old days before there was electricity and camera's. You had to hire an artist and have them paint the situation in oil on canvas, so I have no pictures to post.
However, I have the distinct impression that the battery box is what I folded over and pop riveted in place. Not the floor.
The gauge (thickness of the steel) was 16 gauge so that's pretty thick although it is not tempered so it bends without too much issue.
I believe that I have 1/2" clearance against the footwell side and I might have "shaved" the square edge off of the rack mounts. That's the trickiest detail although I might have taken a big hole saw, like 4" od or so and bored a hole first so that I could get a better picture of the situation. Then nibbled the front and rear until the box would go in, then put a 2x4 or 2x6 block in the bottom of the box and tamped it down, not smashed it down, and let that dimple the box over the rack mount blocks.
Since I might have been drinking wine with my friend Leonardo from his vinyard and not remembering clearly, Merlot, if the dimpling thing doesn't work, you can just notch the box at the interference points.
One of the advantages of this box is that you can use a larger battery with more electrical capacity and reserve then stock. The stock battery size is just going to get lost in the box and look like a motorcycle battery by comparisons.
I do also remember running 00 welding cable back to the starter relay, and then the starter at the same time. The advantage of the welding cable is that it is more flexible then battery cable and the large gauge really helps in really hot restarting situations.