Gobsow, I think you have fallen into the most common misundersanding about patch panels. You do NOT have to use the whole thing. Instead of cutting out all the good metal on your truck for one little rusted area, you trim the patch panel down to just what you need. That is one solution.
The other would be to make the piece from scratch of course. Take a look at exactly where you would be replaceing and make sure it is a compound curve you are dealing with. It could be a flat area or relatively flat "area" in a compound curved panel.
