i need to paint these two 10 foot steel strut channels to go on the roof of my van and it's kicking my ass

my first application of primer didn't adhere correctly, it practically fell off under its own weight

i had to wire-brush the entire thing to remove the bad primer and rough up the surface for a second try... fortunately, my second attempt worked much better:

i've applied the first coat of black paint, but there's a 24-hour cure time between coats (!?) aaauuugh i got started with this on monday, i can't believe this simple project is gonna drag out all week, i should have just gotten the already-painted strut channel even though the only color was weird dark green