Welcome to the forum.
Have you been able to determine what is rattling? That is, is it the screen door? Or the main door itself? Or is it something in the door?
The first thing I would do is have someone pull on the coach door while you are driving to see if it is the door itself or if it is parts within the door or the door latch. If the rattling stops when the door is being held closed strongly I would first try to make sure the door is held tightly by adding some adhesive foam insulation between the door and the door frame. That should be easy to do, inexpensive and easy to undo if it does not help.
If that does not help then I would assume it is something inside either the door or the door lock mechanism. Check the latch to make sure it is not moving when the RV is on the road, and check the latch to see if any parts are broken.
2020 Regency Ultra Brougham, IB model
2022 Jeep Wrangler Sport S toad
Roadmaster baseplate and tow bar