I guess I could triangulate down from the bar, but I wanted to keep the trunk open so I could slide things in if I need to drop the seat. It's pretty solid as it is. As I was tightening it up, I could hear the metal shift and tighten up. Small pops and creaks. Considering all the support I installed under the car, this crossbar completes the box since the subframe connectors
end at the base of the rear wheel well. Running bar down from trunk to around the seat belt mounts wouldn't hold on to much. That would place it above the tunnel where the gas tank is. That's basically just an open box and I'm not sure that area would be a contributor to the overall subframe.
Why I didn't put any washers on the adjustment nuts? I wanted the nut to jam against the one in the bar to help lock it in place, which it did rather nicely. It didn't need the washer to aid in adjustment. The preload on the tower worked rather nicely. I took it out for a run and noticed that a standing stop burnout didn't get all squirly on me. It dug in and ran very
straight. I'd say with the factory front bar, the subframe connectors with improved driveshaft tunnel support, trunk shock tower, polyurethane bushings, and larger sway bars... This car is a beast.
The trunk bar was made with .120 (just shy of 1/8in) cold rolled steel 1x2 rectangular steel. Same steel used on the subframe connectors.