Nothing in a spray can will work because the paint in spray cans are not catalyzed. You need the chemical reaction between the paint, teh harner, and the catalyst to promote adhesion and provide the hardness to resist chemicals. There is one exception out there, and I forget the brand, who offers a rattle can with a vial of catalyst installed in the can. Shaking it up breaks the vial in the can, which catalyses the paint. however, once this happens, you only have a few hours to use the paint before it hardens in the can. It is also pricey, @ around $25 a can.
The other option is having it powder coated.