Take a good look at what you are going to end up with. If you use the connectors that just weld to the bottom of the car you will only be connecting to a small part of the frame in back. If you cut the floor you will be able weld to the top layer of floor that transfers to the back of the car. I have done many of these and the full 2x3 tube with 1/8 is the best and longest lasting way to go.