I do have a convertable. Are supports in the door frames, in addition to the support underneath, all that is usually required for these cars? Sounds adequate to me.
I have, as of yet, not done a complete inspection of the rust damage to the car but the entire floor panel and both rockers are going to have to be replaced, so the the unibody restoration process is more than likely going to be fairly complete.
This, in case you haven't put it together yet, is my first automobile restoration project and I am a little leary of screwing it up before I even get started.