Quote from youme on November 19, 2007, 11:31 am

Mapster wrote:

Also if you use the Portal settings you don't need the func_noportal brush entity for the original textures such as metal walls and so on.

Or infact any texture, official or otherwise.
For official ones simply extract from the game files and change the text file to have the no portal text in, change the name and location and hey presto!