Mike, check out this write up.
http://www.myastroshop.com.au/produc...asp?id=MAS-043
Really it all depends on the 12"OTA, a long one will be more troublesome that a shorter one because of the lever arm effect (wind, vibration, flexure etc)
Then too, a 12"truss dob might create mischief of its own no matter what you mount it on.
best,
Doug