I will try to see what the issue is

Skybox is a missing texture, I have both L4D's installed and mounted.

so I loaded up the map and it seems the skybox is broken cause its just a cube of missing textures. did i break something?

Good to know that we don't have need any game for play this maps :) Do you have planned to port all the Left 4 Dead 1 and 2 maps with The Last Stand maps without we need any games please? It could be awesome ^^ Because I have Left 4 Dead 1 and 2 but I don't have buy the Steam Version because I didn't know about Steam many years ago so when I have play Garry's mod on Steam, I don't have any maps from Left 4 Dead even with the two game installed and there is only Team Fortress 2 model and maps who appear because as this game is for free on Steam I have download it for more maps and it appear.

Neither

al nodes or navmesh

Only the very best

does it include a gaybar?

Sweet!

Left 4 Dead 2 is not needed

Yep! All packaged

Judging by the size I assume content is already included