The world is a rapidly changing and unstable place these days, with the old order and way of thinking disappearing fast (Labour lurching to the left, Corbyn as leader whether he is credible or not?), look around you at the world outside the defence bubble.
Scotland will either be independent, or on the way to it, by 2020. As JiV said, basing any new asset north of the border would be a mistake, and if it is done, it will only be as part of a political game that will ultimately fail at considerable cost!
Where will your follow on SSBNs, if they are purchased, be based in 15 years from now?