I vote for not painting. Somehow, a painted chassis looks cheesy to me.
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
Thanks Radioroslyn & 0Z4 for taking time to comment on this subject. I decided to not paint it and after using navel jelly, just seal the small areas that had rust spots. You guys did a great job on those chassis'.
I'm in the process of installing the transformer and cap can and changing some of the brittle wires.
Will post more pics of chassis when I get the tuning cap back on.
Mike , my vote would be for not painting it. But thats only my 2 cents.
I say no paint as well.
$0.03
Another vote for no paint, but the clear semigloss polyurethane Chris used on his Crosley looked pretty good and will hopefully keep the rust from coming back.