Door bracing is required. A stick of 1 x 1 angle iron is all you need. Cut and drill 6 pieces to bolt to the door hinge locations and the door lock location. Bolt in place then cut 4 pieces and weld them to the previous 6 pieces. Now you are ready to lift the body from the frame. Cross bracing is not normally needed.
Proper balancing of the body on the rotisserie should be done and is important for safety.
All rust repair / sheet metal work though if at all possible should be done before lifting the body. Rocker panels should never be cut out while on a rotisserie or a body lifted with rockers that are severely rusted out.