I agree with Chris...when I bought my 87 5 years ago, my tank, from being
parked over a moist lawn and not garaged or in a driveway, looked like hell!  
I though I surely would have to replace it.  Upon further inspection, I
dropped the tank, emptied it and when I realized how thick walled it
was...like a torpedo for goodness sake, I refurbished it.  First wire
brushing all the old paint/rust off, followed by a sanding and the priming
with an amazing marine primer which I forget the name of followed by several
coats of a gloss off white like the original.  5 years later it looks brand
new!  
Finn Runyon
87 Westy named Pooh