Well, it may be that he only used the mod to avoid the death barrier. Why not give this a shot, and see if it's possible to get into that box at all, without mods? Say, make a trail of teleporters by carrying a receiver node as far as you can before you die, then doing the same thing but starting by going through the last one you made? I'm horrible at describing, so just look up how to get the Sandbox skull using bubble shields to see what I mean.
Thanks to this mod, we now know that the cube exists. Now let's see if there's a legitimate way to get to it.