Well it’s been a year. I’m curious, did you stick with the curb painting business? What paint did you end up using?
I’m a curb address painter. Home Depot sell striping paint in an upside down spray can from Rust-o-leum.
There are ways to paint the black while the white is still wet. Usually two passes over a two inch area constitutes a coat. Since your rectangle is six inches high you will have to do this for every two inch section of the box. If you intend to continue in the this business, I would be happy to tell you anything you would like to know.