There's two products which are used in saltwater environments, and bridge / parking deck steel.
One is Sherwin Williams Macropoxy 646. It's a two part epoxy. It can be rolled on or sprayed. It comes in any color.
A two-component, high-solids, fast-drying polyamide epoxy mastic.
industrial.sherwin-williams.com
The other is Sherwin Williams Corothane mio aluminum. It has aluminum solids which apparently inhibit rust. I believe it requires a topcoat.
A single-component, moisture-curing, aluminum and micaceous iron oxide (MIO) filled urethane primer, intermediate coating or a finish coat.
industrial.sherwin-williams.com
While both of these products are listed as industrial, you can go down and buy them from Sherwin Williams. The marcopoxy is $90 a gal retail, but it can be bought as low as $40 a gal with a commercial discount.
These two products are far, far superior to POR15 or any Eastwood product.
Excellent job with your truck!