I have a 45 gal tank/toolbox with an electric pump into the filler neck. The switch is mounted on the front of the dash and out of the way. I tried gravity feed, but took forever to get the last 5 to 10 gallons out of the tank.
Make sure the tank you get has a bung installed where you can pipe it out to your stock tank. Some transfer tanks come with no bung as they are used to mount a hand pump on top for transferring fuel to machinery.
I paid $550 for my tank from a local truck parts dealer who also installed it. It's stamped diamond aluminum. The electric pump was purchased from Auto Zone for $45. Filter was $35 and also from AZ.
The advantage of the extra fuel tank is traveling from state to state, the fuel prices will vary up to .50 a gallon. Buy when the price is right and drive through the areas where it is high. I generally buy from FlyingJ/Pilot with their card which gives an extra .20 to .25c discount on diesel.
2013 Silverado 2500 HD Duramax/Allison Tuned
Aviator Wright Flyer #1919
"First In, Last Out". 11B4Y
DAV, MOPH, VFW, 5/7 Cav,1/8 Cav Assoc.
11th ABN Pathfinder Co. N7MIP