1) Compile your map to maps/foobar.bsp. Do not place it into a different folder yet.
2) Run the map using the console command map foobar.
3) Run buildcubemaps.
3b) Run buildcubemaps for the other light setting. (LDR/HDR)
4) Move maps/foobar.bsp to maps/yourfolder/foobar.bsp.

Now you can run the map using either map yourfolder/foobar or using the Bonus Map interface if you have BNS's set up, and your cubemaps will work.

Caveat Emptor: The above procedure worked for me. If it doesn't work for you, post about it and we'll see where we went wrong.

Try buildcubemaps on an official map - it will tell you that it can't because the official maps are write protcected.

(hint: the information in the original post has been available on SDK wikipedia for ages)

Korjagun wrote:
4) Move maps/foobar.bsp to maps/yourfolder/foobar.bsp.

Now you can run the map using either map yourfolder/foobar...

One question: Did you close Portal?

If you didn't, start the map again. Because some days ago msleeper and me found that when you buildcubemaps in the maps/ folder and then you start the map on a subdirectory, even if you don't buildcubemaps the subdirectory file, it works, if you don't close Portal.

Hurricaaane wrote:
One question: Did you close Portal?

It works even if you start the map fresh after closing and restarting Portal.

Just to be safe, this is what I do:

1. Compile map and leave it in default maps folder
2. Open, make sure it doesn't create any saves
3. Run buildcubemaps for LDR and HDR (this will create a save file)
4. Completely exit Portal, delete all the save files for the map and move it into the correct folder
5. ???
6. Profit!