There is a "Certain Settlement" that once taken over "in a certain way" does not allow you to move the previously placed turrets/beds.
If you want to move these turrets/beds, just open the Workshop, highlight the object, and HOLD the "activate button/key" (X on PS4).
Then you can move the "owned" beds wherever you want, and place the turrets outside the wall and destroy them (for the loot) and still have access to the locations they were in to place your own turrets.
Some objects in "this settlement" are still not able to be moved...Beth seems to have made them part of the permanent world.