There are all kinds and sizes of "slam latches". You just need to find one that fits the configuration you have. What year/make/model of RV are we talking about, and what sort of latch does it now have? A picture might help.
Here is one source for slam latches:
Thanks Tom great site. I been thinking about doing this also.
Now to figure out which to get. Be nice if they come with keys nobody else has in the park. ;D
Not that any one has ever walked away with any thing.