Ive done a whole pan.

I set the car on jack stands supported by the frame rails (pull tires and wheels and just let the suspension hang ) then carefully measure the distance from frame rails to floor ( was sitting on smooth and level concrete btw ) And cut some 3 " square stock tubing and tack welded to the frame to the floor to prevent ANY sag once the entire floor was cut out.
And replace the pan with one piece.

Might be overkill, But Im of the mind better safe than sorry