I think you've oversimplified that greatly. I've done that with quarterpanels, using the fenderskirt as a tracing guide. Working with the double/triple layers of roofskin, structure and dutchman panels spotwelded together, and then having them reasonably correct (for the glass to seal), and getting all the clips back to hold the trim tight enough, is a lot tougher. Especially if some of the metal is gone already. But at least you are standing up while you do it.