Gotcha, wasn't sure if it was just a camp junk trailer your pulling. Those side mounts just dont sit well with me for whatever reason, but its not me jeep either. I've never used those hi tech plastic fuel holders, but I will say when your bouncing around and its hot, the fuel will expand and leak out of the GI cans which is all I ever use. So think fumes and fire potential where ever you mount them.
I had one of the Dirtworx spare/can carriers on a YJ, but I dont see them on his website anymore. maybe you can give him a call and ask if their still being built. None the less it came at a cost. But they are a item you'll not regret having in the future and it keeps the tail gate from destroying itself.