I used Chassis Saver and I'm pleased with it. I bought the gallon, on the advice of the salesguy and it turned out to be WAY too much for just the frame and axles. I intend to paint the underside of my tub and everywhere inside of my engine compartment as well.
Durability is high as far as not being scraped off. It is marred thought. I had my frame painted and on stands so I used it as a stand for rebuilding my axles. A fully loaded Ford 9" is heavy and a fully loaded, full width high pinion Dana 44 is REALLY heavy. They left marks in the paint, but they didn't gouge through to the metal.
I used the silver with a brush and roller. I wish I had sprayed it on instead, but for what it is I'm pleased.
As far as usage being minimal, I have well over 2/3s of the can left so I know that I'll be able to cover the rest of what I want to cover. That'll keep it bright for nighttime repairs and it'll keep it from rusting a little better than an easily chipped paint would. I intend to do the interior in Line-X or Herculiner next Spring.