This was a surprisingly quick, easy and cheap undertaking. I found most of the materials at my local dollar store, from the American flags to helmets to the heavy-duty duct tape to the moss. We did already have an arsenal of Nerf guns, so that might add an extra level if you aren't so equipped.
I just slit the one side of the box and then taped up all the flaps to form the curved shape. I cut the openings with an box cutter. It was a fairly sturdy structure,even as simple as it was. I think it's because I used strong moving boxes. Results may vary otherwise.
I found the "ammo crates" at Target, in the bargain area.We have a ton of darts thanks to Amazon deals, which I recommend, particularly in this scenario.
I wanted something that would stay together, but was flexible enough to be picked up and tucked into the garage. This worked perfectly.
Did they hold up in actual warfare? See for yourself.