Permanent support may vary by particular job and specs. For this one there were some A&M Steel brackets added.
http://www.aandmhardware.com/regular-brackets.php.

The top you see is the sub-top. Final surface was Corian.

The desk was covered in cardboard right after my men installed it and by the time the cardboard was removed we were long gone from the site, which is way down in South Miami about 1 1/2 hours from my shop, so I haven't gotten "finale" shots yet.