I think MSP J Barracks can transmit from the huge antenna tower located at the MNG Armory along Rt 50 just east of Rt 450/West St. One scenario is the the south AACo Troopers continue to use the same frequency as they do now, but the control point is at the Glen Burnie Barracks.
As far as police service goes, losing the Annapolis Barracks probably won't hurt that much. The former trooper who lamented losing the Annapolis barracks tried to support his case by pointing out the assests in the Annapolis area that need protection - the state house, the Academy, the Bay Bridge, etc. All these assests have their own police forces, in addition to the larger Annapolis and Anne Arundel County PD's.
The downside to closing the barracks means that administration is a long way off if your patrol area is in south county...