Be cautious when mixing metals. If your door frame is steel use steel. If the door frame is aluminum use aluminum.....
When I got my Toy Hauler when it was brand new I saw daylight between the gap in the door. The door was not sitting square in the opening. With daylight showing I knew this was a potential way for water to get in. I really did not want to take it back to the dealer even though it was under warranty. I added a strip of 1/2" steel angle to just the left side. My door frame is made of steel. I used a little silicone between the two surfaces and screwed the angle iron to the frame. Later stood back with a garden hose, no leak.