The easiest thing to do is to have some school-age children around your house. They will sometimes have assignments that call on them to use these things:
You can build most tournament maps right on the back of the middle section. Voila! Not only that, but - once you've removed the trees & whatnot - you can then build a second map and stack it on top. That's what we do for tournaments, and I believe in a pinch we've stacked up to 4 that way. Though if it's a heavy load then I use a piece of plywood I cut into that shape to hold the bottom map.