[T3] Fuel System (Tank)

[Jacob Schroeder]

While my car was sitting in storage for the last five years, the
fiberboard became wet and this moisture has caused the top surface of
my fuel tank to develop some rough, rusty patches.

Because I am going through and replacing the fuel lines, should I go
ahead and pull the tank now and have any rust removed?  Last time I
checked (~ 7 years ago), the tank was completely free of rust, both
inside and out.  But I know a lot can change in that time. If so,
what's the best way to clean up the rust?

There is still 2-3 gallons of (old) gas in the tank, is it ok to use
this or should I dispose of it?

Should I worry about checking/replacing the activated charcoal filter?
 I'm sure this has never been done.

Finally, does anybody know where I can find a replacement fiberboard?
I'm totally bummed because mine was perfect before it sat, now it is
ruined.

Thanks in advance!

Jacob
'72 Squareback