A while back someone asked about powder coating exhaust systems and
someone else suggested simply wiping the  exhaust system with Peanut oil to
prevent rust.

  I've done that twice now with my custom headers and exhaust collectors on
my inline VW motor in my van and it does work quite well.  I think if I had
done that from the first, before any rust got started, I would have been
totally happy with it..  There was a section of real rust starting on one
corner of the primary collector and that still gets a little rusty after a
few weeks...I am going to scrub it down to bare metal again and re-oil
it...see if that works.    The rest of the pipes, where the rust never got a
good start... they've taken on a nice a nice clean gray color and do not
rust at all.  I live in the Northwest, so they do get wet often.

  I like stuff like that...low tech, cheap, easy...

  Don Hanson