Tablo has stated in the above thread that the safe operating temperature of the Tablo is 41 to 95 degrees Fahrenheit so it would be too hot in an attic. I would be concerned about moisture in ductwork. #2 might be your safest option.
As for the antenna, height and a clear line of sight are very important factors. An attic antenna should give you the best results 2nd to the roof, but if you’re pulling in 65 channels you shouldn’t need to worry too much.