What's a good clear coat for bare metal for both inside and outside conditions?

I've used Penetrol a few times. So far after a year of so out in the Texas weather (hot, dry, damp, hot, dry) it's holding up fair. What I don't like is that it takes a long time for it to harden up it seems. And I doubt it will last that long.

Anyone have experience with Permalac? http://www.permalac.com/html/Metal.html

Thanks,
Floyd