Try using this console command:
sv_portal_placement_never_fail
Portals on moving surfaces?
4,095 Posts
Posted Oct 11, 2007
Replied
41 minutes
later
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307 Posts
Posted Oct 12, 2007
Replied
4 hours
later
This is why i'd probably wait until the official SDK.
Prefabs and SDK VMFS. 
33 Posts
Posted Oct 12, 2007
Replied
2 hours
later
they don't HAVE to do SDK VMFs, hehe. Besdies, better pratice to do it early .