Ok, so, I have been looking around at various seeds to get Mansions. All have been tested by a variety of people, yet I cannot seem to get them to load. An example seed is 2710604025723660192 where there is supposed to be a Mansion with a portal inside at -400 100 1400. Odd thing is, I get a portal, but NO Mansion anywhere. 
I DO have Structure Generation set to ON. Still, no Mansion