Good shit, Whippy.

Anyone know how I can do this?

It's just a death barrier to prevent players getting outside the map, or in unplayable areas.

You can group brushes. Press B to go to the Entity Browser, go to Func and drag "Group" to the 3D window while your brushes are selected. You can select the entire group with Alt SHIFT Left Click. You should right click on Group and favorite it  though so all you have to do is right c...

Congrats on the release, well done.

Good layout and everything but really buggy.