What scale? What is "a large number"? How many feet of walls, how many towers?
My first idea is to make each wall with three pieces; front, top and one side. One end has pegs that fit into holes on the other side. When you fit them together the single side will support everything, but you can take it apart and nest all the wall sections together. You will also need to make inside and outside corners for bends, and set up your towers with matching pins and holes.
Personally, I would just use blue foam and set things up so that you can fit it all in banker's boxes or something similar. Wall section lengths equal to the width of the box interiors, etc. You can fit a _lot_ in one of those boxes if you plan well, and they don't take up much room.