It might be easier to pull the bed, it doesn't have to come all the way off, just tilted up on drivers side. Loosen right side bed bolts, remove left side bolts and filler neck, check and/or unplug wiring at the back for lights and trailer. Remove items from bed and tailgate to reduce weight and lift bed up with some help, have wood blocks or something to wedge bed up in place.
Pulling the bed can be easier since you don't have to deal with laying on you back, dealing with a long skinny tank of fuel. Plus the fuel line connections can be a PITA from the bottom. I've done them both ways and would only consider dropping the tank with a lift and trans jack for the tank.