Here is the bed of my '37 which I restored in 2015 to 2019. At the time Mar-K recommended an oil based primer followed by Behr black paint from Home Depot. This is before I recall any recommendation to use POR-15. The paint is essentially perfect at this time but I must confess this is the one truck that gets babied. It does get washed, see occasional rain, AZ sunshine at times but very little cargo work. I have 4 other trucks to do that.
I have a neighbor who has an '84 Chevy step side and it came with bed boards painted body color (red). The paint didn't last long in normal use.
