OP, my setup is just what you are proposing except my aux tank is 41 gallons. It measures 11" front to rear and sits below the bed rails. I have a bright indicator light that shows when I am transferring. Make sure your electric valve is on an accessory circuit or you may find you are transferring when the truck is off. I have the Fuel Shotz system which is safety float type shut off valve as a backup.
Most of my trips are 100 to 300 miles, we stay a week and return. I don't have to refuel on the road and wait until I'm home for less expensive fuel. After 3 years I figure the tank has paid for itself in fuel savings. From now on out, it is money in my pocket. The tank is a very good add, as I never stress about low fuel on the road.