I used oil based from Home Depot on my open deck car hauler diamond plate, primed first.
Then some anti slip from Napa where the wheels track.
This Is the only picture I have of it on my phone. It’s held up well 2yrs so far.
I have used a good quality stair paint. Has sand or grit in it...holds up well and makes for a non slippery surface that is durable. Usually lasts about 5-6 years.
Used anti freeze works well too. I apply it with an old garden sprayer. Keep pets away until it dries (or cover with a tarp). Even though it sits outside my 20 year old equipment trailer still has it's original deck. Also solves the problem of getting rid of used anti freeze.