Boarding Party

First off, head to the waypoint in the trash area. You'll see a big pile of garbage you can use to jump over a barrier. Once you're over, find the bin with the lock on it, break it open, and grab the ECHO inside.

Next up is an ECHO on a dead body hanging above the area. You can't reach it directly, so find the platform the body is hanging from and shoot it. The body will fall, letting you grab the ECHO.

The third ECHO is located inside the storeroom where you got the Claptrap unit during the 'Home Sweet Home' mission. It's stashed away in a locker, so just open it up and collect it.

Finally, the last ECHO is perched on top of a waterfall. You can't just jump to it, so you'll need to find a hidden switch. Face the waterfall, then turn left and hug the wall. You should find a highlighted switch along the wall. Hit that switch to open a path that leads directly to the ECHO on the balcony.