[OZ4]

I don't much like the painted look either. If the chassis is really pitted then after doing some body work with a little filler I would use a metallic paint but not bright silver. Just look around there are lot of metallic paints now. If their too bright just dust them with some grey for toning down.  As for preserving the metal from rust and since the original finish is gone this is the only place I would use clear polyurethane. It holds up better than lacquer under humid conditions.

Here's one I did that way. http://philcoradio.com/phorum/showthread.php?tid=10465
Good luck