This stuff is tough as nails. I used two of the aerosol cans on my Dnepr frame and no rust almost two years on. My rig has to live outside, too.
I painted the car body with the POR15 rust preventative paint and top-coated with another of their products and no rust on the tub either.
Cheaper than powder coating. Not as hard, but harder than anything you'll get off the shelf at Lowes or Sherman Williams.
You have to follow the directions to the "T" if you want all the benefits.