Metal frame sits very securely in boot using only 2 bolts in pre-existing holes.
I removed the 2 child seat restraint clips near the tailgate lip and used the (already threaded) holes for the bolts.
All the smaller bolts you can see on the frame are just holding the frame together.
Had to take care to avoid the 4 footman loops in the back of the tub.
The front of the frame is flush up against the middle seat belt bracket and the sides of the frame are hard up against the sides of the tub and slide under the backseat catches so the frame cannot move sideways, fore, aft or even up and down.
Run some cinch straps under the frame...
And tie down sub
It's a tight fit - the rub marks on the straps are from the tailgate.
But the rear seat still fits and the frame doesn't hinder the operation of the seat latch.
Also - I'm using one of the bolts as an earth for the sub.