I've got a surplus Canadian military can, looks the same as yours except it's green. Has a red tether for the cap, they also come with a yellow tether for diesel.
I carried it full, inside the Jeep for a 3500 km camping trip and it never leaked. Almost needed it once but managed to find a gas station in time!
I like the brackets though, would like to find some of those up here!
Oh, and that mortar box is cool! I'm looking for a larger steel ammo box to mount on the front of my utility trailer too, seen one once a long time ago but haven't seen any since. The small .50 cal ammo cans are readily available here.
Dave