Just mount the tank on a rear rack as high under the seat as possible. (Above the carb!)
Get a zippered lunch cooler big enough to fit your stock tank and punch a hole for the fuel shutoff valve to poke out. Mount tank in the opposite direction you normally would. I used a chunk of wood to mount the tank to the rack . The wood was under the hump of the tank, inside the bag so you could not see it. This allowed me to use the original mounting hardware that came with the tank. The studs poked out of the bottom of the lunch bag.The fuel line will come out right under your seat on the left side, inches away from your carb.
Everyone always asked me where my gas tank was!