I have a truck with a steel tilt up deck I haul hay with that needs new paint. Its all channel iron with that expanded metal mesh on top. Now originally I just used your standard cheap IH red rust paint from the hardware store and sprayed it on DTM about ten years ago right when the deck was built (new metal). This time I want to go with a better paint, primer and blasting. What is used on construction equipment and trailers now days? I know up here in the oil patch stuff like Endura 2k polyurethane is a common choice. I'm sort of deciding between that system or going with a good primer and some better quality enamel like the machinery enamel from the dealer or say Nappa. As I found in years past the endura though very hard is not immune to rocks and other things hitting it and chipping it off which will happen on this unit. Then the rust starts to get in there and screw things up in the end anyway. With an enamel its easy to just "touch it up" once a year with a brush. This truck is stored inside when not in use and doesn't get many miles on it a year 7-10K only.
Well I'm a big fan of POR 15, its hard and durable, but takes extra steps and needs to be topcoated. Another one I use a lot on frames and beds is black from the local cat dealer. Its an enamel and pretty good stuff as well, and reasonably priced.
Second the POR 15...I used it to coat the floors and trunk of my '39 Chevy and after 13 years it's still holding up.