Follow up on this.
I see now that I was overthinking the whole putting the floor in the van business.
I ended up just laying the boards, and I'll probably use L-brackets on the factory tie-down points.
This wood isn't particularly long lasting and it'd be inconvenient to attach it permanently.
I also put some plywood panels on the sides.
Now it's functional for my needs, but there is still plenty to do.
https://imgur.com/a/JHNLPtc