Lease the facilities from Scotland
Why pay billions to Scotland that could be used to build a new facility? Uncle Sam will provide at cost (or for free) what Scotland will charge an arm and a leg to lease. Your statement suggests that you believe the Scots will deal in good faith. Actual SNP rhetoric indicates a philosophy not very different from Venezuela's late Hugo Chavez.
Salmond has his own plans to turn the sub base of Faslane into the HQ for the Scottish Armed Forces.
Moving the subs out early would probably be a good idea for both sides, and on a much better timetable than mentioned below.
From a report on the last debate -
Alastair Darling said removing Trident would mean a loss of 8000 jobs. But, replied Salmond, we plan to keep Faslane as the base for Scottish Defence, with all the jobs that implies. Darling countered with the Royal United Services Institute’s claim that Trident couldn’t be moved until 2028. Salmond came back with the fact that RUSI actually said that setting up all the infrastructure elsewhere for Trident and its submarines would take that long. The removal of Trident could easily be accomplished in the proposed 5½ years. The fact that no one could use it for several more years would be to everyone’s benefit.