Ok, I have repaired these types before and there is no easy way of saying that you really need a patch panel.
You can make it yourself if it is not offered, but I don't know of any vehicle that was in mass production that they are not offered for at this time.
The reason for the patch panel is because the metal on the inside will be just as rusty as outside. You will also need to gain access to the inner door shell to clean and seal it from further rust.
The only good way of repairing rust areas is to cut away to clean metal.
I found a product that works great at killing rust in conjunction with POR15 to seal it off. I use a product call RUST CURE in a gallon jug. It's green like Ospho, but 100 times better. I have sugar blasted cars and coated with this product and left them raw metal inside my shop for a year without any surface rust coming back. I live in the Gulf Coast region and if it was not a good product, it would show quickly.
If you don't want to redo this again, cut it out and spot weld in a new panel. To keep from warping your door stagger your plug welds and let cool after each one. A little more time, but will save a ton of body filler repairs to this area. If you can get some welding clay, that would be a better plus. If you want to go high tech, you can panel bond to the upper portion and spot weld the corners. This would be my preferred method.