As far as I know, encounters are "open" for 60 minutes, meaning a player can find it during that window. After the window is closed, the location cannot be found.
What we used to do was load up people in a caravan cart and spam the map until we found a map we wanted, usually the big warehouse looking one. In 2238 the encounters were only open for 10 minutes or so, so it was easier, but the concept might work the same.
You just have to defend it a little longer. It's not as secure as a tent map, but it's easily doable. We had several of them the entire last 2238 wipe, and everything was fine.