Use it to store jerry cans concealed and semi-protected? If you lay a jerry can on its 'back' (like laying a book down on its spine), its footprint is approx 18.5" x 6", so 4 cans would fit almost perfectly in there. In that configuration they're about 13.5" tall, so you'd have a few extra inches of vertical space. You could use that space to build a pad of some sort for them to rest over or under to keep them from bouncing around. I'm thinking you could glue some foam to the lid that would kinda compress down on them and hold them firmly in place. That whole project would probably only cost a few bucks. Throw a lock on the hinge and you'd have a pretty decent storage system.
EDIT: I just had another thought. If you set it up right, you might be able to fill the jerry cans while they're in the box. Just put them in there with the lid on the opposite side from the hinge. You might also have to put some sort of foam down at the bottom to raise them up a bit as well. Depending on where the box was mounted, you might never have to remove them if you use a SuperSiphon with an extension to reach the filler neck.
