I mounted mine by just drilling through the floor and placing steel plates under the car to prevent the bolts from pulling through in an accident. HOWEVER, after seeing a few accidents it's clear that the floor buckles and twists which moves the seat, usually towards the door. This puts the head close to being out of the rollcage area which can be very ugly!
I have seen seats mounted to the tunnel and doorsill which looks a lot stronger. If anybody can show us an easy way of doing it this way, I think we are all better off.