i am using a stock 20 gallon jeep cherokee tank..it will fit nicely between the frame rails where my spare tire used to be
my tank is a bit newer so it has more vents and stuff, so there will be more capping off of lines for me
but basically it breaks down like this for me
fill tube
vent tube
external pump wired to a switch
return line
gas line
its pretty simple, just some fabbing to hang the tank securely and making a skid plate for it.....
if you want to get super cool...you can use the stock pump and sender and hook a gauge to the sender and have a fuel gauge as well

..just wire a switch to the pump..but an external pump would be a bit easier
rob had a part number for a good external pump, i just dont know where i did with the part number