I decided to seat the floor panel in a small bed of JB Weld where the torque tube bolts down. The edges are covered by the passenger arm rest, so it won't look unsightly if there is a screw holding down the edge further forward and it is important that the flap torque tube is mounted square.
I prepared the underside of the floor with mould release wax and PVA, then also waxed the 10-32 bolts to ensure I could remove them easily too.