I doubt this has anything to do with the Bin Laden tape or a terror threat.
The fact that these type of measures are being encountered at this base and no other base (they we know of) indicates something specific here rather than a general type of alert.
Preparations for a possible North Korea ICBM intercept seem the mostly likely giving the timing of this and current events.
Could also be something less dramatic such as the installation/construction of new base facilities.
let’s hope for something “less dramatic”
FWIW - Gates was in Alaska the other day. Maybe checking out the missile defense site there?