Oh my stars, I'm sorry for posting about the screen door when you meant the main door catch.
At anyrate, most RV manufacturers went to the plastic door catch, because the usual stuff was made out of mild steel... which rusts. No one wants rust stains running down their gelcoat.
However, if you need to replace the catch, perhaps you would want something in stainless steel... THAT doesn't make it rust free... just less likely to send stains down the side of the trailer. It's still a maintenance issue.. pay attention:
Amazon.com: RV Designer Collection E224 4 Inch Stainless Steel "T" Self Closing Entry Door Holder: Automotive