Prior to starting the project described above, I did some internet searching for the strength of nutsert / rivnut and other blind hole fasteners.
I found threads where some one had installed a roll bar and used nutserts to mount it to the floor, failed NHRA inspection, other threads where blind hole inserts were not considered strong enough for sway bar mounts,, general consensus was, they are great for panel mounts, other non critical applications, but it’s your car, do as you choose. I believe the ‘pucks’ as installed would be at least as strong as a welded on nut.
