You'd have to screw them togeather to keep the lids on and paint them...but they're plenty tough. The price is right in my neck of the woods, though. Not as common as pallets but theres a lot less competition for the resource....
Or you could do a similar thing with purpose built modular blocks in, say 1x1x1,1x1x2, 1x2x2, 1x4x4, 1x1x4, 2x2x2.... to maybe a 4ft cube. Light and easy to move to reconfigure the field, easy to replace if damaged, could be nested for storage.
Or to take the idea of an old field i used to play at, a sort of cross between a sawhorse and a temporary highyway divider with notches so they could be stacked and interlocked in multiple ways.
Some of the crates/ barriers could PURPOSELY be skinned with a couple layers of cardboard so that under a steady barrage they would degrade to discourage camping.... might be better suited to scenario games though.