I used 100mm square plates under the rear seat mounting bolts to spread the load in case of a front collision, as surely the seat would want to throw forward (regardless of seat belt anchoring points) and I wasn't convinced the floor panels by themselves were of sufficient strength. No questions from the IVA man.
Although by spot welding the bolts to the seat runners I could just drop the seats into the holes into the floor panels and bolt them from underneath the car. Simples