I cut open the panel over the rear mounts again.
Found this large crack also
I welded in the 2 side plates again like before to see what difference it would make
I didn't do anything else or repair any of the welds or weld on the reddish plates at this stage as the car is still together and I wanted to see the difference these 2 side plates would make.
This time you can see that I'm really trying to move the boot floor. Lots of revs and being aggressive with the clutch
https://youtu.be/n_vUb6YAxeg
Plates on the bottom would have had no affect on repairing this at all.
Bottom is very bad also
Cracks drilled and welded up