That's a Hehr brand vent, and was standard on the Trilliums. As far as I know, they're pretty robust. It opens by pulling a chain that hangs down inside the trailer.
The vent I'm planning to replace is on a Boler
. It's not the Hehr vent you have. I think the one I have is plastic (and may be the Elixir Mini-vent). It also looks as though it has been replaced at some point since 1974.
I don't know if there was ever a "standard" vent on the Bolers like there was on the Trillium
In any case, bet that Hehr vent is pretty robust -- I know my Hehr windows
are still going strong. I wish they still made that vent, as I'd install one in a heartbeat, but as far as I know they no longer make it