MOPED ARMY

As far as gas tanks go, I've seen some pretty gnarly ones made out of fire extinguishers. You could even just bolt/weld on a fire extinguisher bracket (or two if the tanks are small), and have removable tanks. You would have to add a fuel outlet, but thats easily taken care of with some creativeness.

I've been wanting to make a cafe racer using one of the long jawa step through tanks. The only problem with that is that the filler cap would need to be relocated.