The roll bar regs require a bolt-in cage to have backing plates at the floor mounts, so I looked for a suitable mounting area that would require minimal reforming. The soundproofing came off easily with a heat gun and scraper, then a bit of thinners to clean up the residue.
Mounting point - note depressed area
Rather than work around the depressed area, I reformed it with a hammer and dolly.
Mounting point - reformed flat
To allow the mounting plate to sit flat, I also removed the seam sealant.
Mounting point - drilled
The RH backing plate includes a hole for the stud used to secure the underbody cladding. Mounting screws are aviation grade countersunk 5/16" machine screws. The 100° countersunk head conveniently avoids countersinking to a knife-edge condition in the 3/16" backing plate.
RH Backing Plate Installed
Th LH backing plate has an additional conflict with the brake and fuel plumbing.
An additional clearance hole is needed for the stud securing the tubing braket.
Plain nuts were used for fitting purposes, but self-locking nuts will be used on final installation.
Measuring for the carpet cutouts is a challenge. The cutouts were made with some sharpened steel tube. The vertical slit in the carpet allows the carpet to be installed around the hoop tube.
The result is quite neat. The carpet foam backing is quite thick, so it is necessary to mount the main hoop about an inch forward of the bulkhead if you want to do this.
The rear stays pick up an existing 12 mm bolt.
In place, minus one of the stays. The hole in the front of the main hoop is a required inspection hole to permit confirming the tube wall thickness.
Next stop, powdercoating.