Alan, mine has the same slider that goes over the aluminum bracket that is welded to the screen door. I am planning on replacing it with the same spring loaded catch that is used as a door hold back on my coach. It will retain the door while closed and assure me that when I open the outer door the screen will go with it.
From Inland RV's site, but they are available at any Airstream dealer:
Latch, Plastic, Main Door Holdback, Used with Part #18781 (Note: Parts #18777 and #18781 are now used for the screen door to entrance door latch. You may have to fabricate a shim)