I need some help and guidance.

The rubber donut gasket on the gas tank where the filler pipe enters the tank is
leaking. My van is a syncro so the gasket location is difficult and awkward.
Keeping dirt out of the tank is going to be difficult. Just getting the old
gasket out will be a PITA.

What I need to know is:
-how to keep the dirt out,
-what lubricant to use on the new rubber gasket,
-how to treat the inevitable rust on the filler pipe,
-any tricks or warnings that I should be aware of.

Any and all comments are welcome.
Thanks
Larry