Wankel Shop Germany Rear Strut Brace for non-OE to OE
 

It makes the non OE rear dampers connect back to the C-pillar frame for stiffening, just like the OE strut setup. Less load will be put to the floorboard which is welded as much as glued with adhesive, not ideal for load bearing.
Bracket is made from thick welded stainless steel to transfer the load vertically. You will need nut, M8 or M10 bolt, washer to tie to OE bracket.
https://cimg7.ibsrv.net/gimg/www.rx8...a5bfec1106.jpg
Right side installed in place, left side uninstalled.

Left side was slightly pushing out the factory U bracket but put back in as U bracket was tightened down.
No issues with fitting to the trunk floor. Just had to make sure Sat radio cables were clear on right side.
​Shipping from Wankel shop can vary base on your country's custom BS. Actual shipping itself was quick.
Wankel Shop also sells bottom braces to fit under transmission tunnel, made in stainless steel.

clearly you’re not an engineer, or at least not a competent one.

perhaps you can step up and make one with vertical fold in the stainless steel, or weld in a rib perpendicular to the vertical plate.