Each manufacturer and model is different.  On my Triple E, I was able to cut a 11" square access hatch in the floor, under the rear bed, to easily access the fuel pump.  I can now change that pump in 30 minutes if needed, no jacks, and no need to crawl in the mud, or find a place to store 50 gallons of gas! Also, the bolts and fasteners on a 20 year old tank are going to be rusted and frozen, not a nice job to tackle if you need to drop the tank.
BTW, if your pump is beneath the water tank, well, its likely easier to empty and move the water tank than the fuel tank.