I understand your desire for portability, but "rolling up" ground cover and foliage, IMO, will result in loss of the ground cover and foliage damage in the process.
I agree that modular is the way to go. If you don't want to go quite as far as Monsoon's approach (just ground cover and foliage w/o any buildings, vehicles, people, etc.) you might think about storing your ground cover modules in a vertical, wheeled stack cabinet such as may be found at any office supply store or Ikea. They come in a fairly wide variety of widths, heights, and depths, and are relatively inexpensive. And they offer a good storage system for all of the miscellaneous stuff one accumulates in building and operating a layout, too.
Poppyl
