Oh man, I was assuming that you were building cubemaps correctly >.<

I don't think you really need to reload the map 2 times though as the wiki says. Just:

buildcubemaps
mat_hdr_level 0
buildcubemaps
mat_hdr_level 2

ALWAYS do that way

You might also need to use console command mat_reloadallmaterials in main menu after you have built cubemaps. Or, alternatively, restart the game. That way the cubemaps get packed into the .bsp.

The separate computer that I have been using to test whether the cubemaps work has been down a few days. If anyone can check and tell me if it worked, that would be great. I put a link to the workshop page in a previous comment on this thread.

Cubemaps look fine to me.

thank you.