I could totally see making some braces for the door openings if you were removing the body from the frame (as it would have a tendency to twist without the frame for support) or if you had a convertible because there is no roof line to help keep things in place. Heck, I would completely brace the body internally if I were removing a convertible body from the frame. Don't want it going anywhere.
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-Douglas Adams, Mostly Harmless