The front crosspiece support is bolted to the seat anchors under it, unlike the same crosspiece of the previous design (it just sat on the carpeting). The crosspiece at right is sitting on the carpeting and has shims under it.

The space under the overhanging 2x6s is where I store my tripods during road trips. Some tools go in the space between the two crosspieces.

The next photo is a close-up of this end of the bolted support crosspiece.