The only way you can get a more definite answer would be to get one from the manufacturer of the tube showing the load bearing capacity of a tube in a cantilever of 12", or of course you could consult an engineer, but theyre going to ask for many more answers before they give you one:) Sorry I couldn't be of more help.

Incidentally where did the 3 1/2" specification come from? . 

If it is over 12 inches must have extra support or 45. to hold the weight

Thank you mr Ortiz, now where did you get that information. Do you have a verifiable source ? I think what we are after in this is a source we can point to that says that. Manufacturing documentation, engineering opinion or other written source?