It can be done with the tank in the truck, but I highly recommend dropping the tank, and setting it on the tailgate to do this. It ensures you get it to seal properly during re-install, and should be harder to destroy the lock ring when you're able to, you know, see what you're doing.
Also gives you a chance to check for sediment in the tank, change the 22 year old hose clamps on the fill neck, and inspect the vapor roll over valves. Popping one of those will also help you line up the return line rubber stopper when you're re-installing the sender.