Well, I wanted to try something a bit different (And I made this for a project that kind of went nowhere -_-), so I took some of TheMask's scene-building props, imported them into Blender, and I made it into one large prop-box.
It works like one large prop, so I'd recommended setting up your scene in one of the "Stage" maps, then switching over to a void map, or anything that has the sort of sky-box you're looking for.
It should work in GMod as well, as I made the physics model the floor panel, and it seems to be fine for me.
I did alter the original materials some, as the trees looked like they were radioactive under some light. So, just let the pack over-write any of TheMask's scene-building materials, or don't if you have made any changes to them yourself.
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