Mount the rear hoop t o the back seat corners. It is very strong and has three sides to attach to. The front tubes ca n be put through the speaker hole on the driver side and straight down on the pass side. (Shorten the tube).
The front plates should be on crush boxes for the floor and run up the rocker sill. Dont weld 360* around the floor plates. I t promotes punch though. Look on the back side of any floor plates and you will see what I mean.
If you run the main hoop inside the door post about 2 in, you can get a nice, single bend, for the door tubes.
HTH, MM