This topic has been discussed before and you can find lots of information using the search tool at the top of the page. Weeds has done a nice job documenting his restoration of a Suburban, which is similar to your panel.
Here is a link to his album
Richard's Suburban I did not notice any extra bracing on his Suburban body as it was removed from the frame. I have seen others brace it at the doors and at the rear before they removed it from the frame.
