There was an extended discussion of just this question on the air-cooled
VW discussion group recently. The vast majority agreeded that chemical
dip was not a good idea - even with cleaning some of the dip always
remains behind and causes rust, especially at weld points. Several folks
spoke from personal experience on this point, telling about rust under
paint after two or three years.
On the other hand, I had the fenders and hood of my 62 Bug dipped eight
years ago before repainting and they still look good. Of course, these
parts had no welds and were easy to clean (no hidden cavities). So, the
lesson appears to be: dipping body shells is bad, dipping body parts can
be good.
I've read recently that there are new types of sandblasting that use
plastic rather than sand as abrasive, reducing warpage or flat panels.
This might be worth looking into as a time saver.
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