OT rant about keeping '77 B200 camper on the road; then a fuel filler question

Bill Crowell said
What kind of hardware is necessary to attach the 2" filler tube to the tank, using the rubber grommet mentioned above?

Nothing. Simply clamp the pipe to the filler neck hose and slip the pipe into the doughnut. As I stated, the pipe needs to be a big enough OD that it will fit tightly and seal good.