Steven,
I finally painted my cage last weekend after it had been built for about 3 months. It had started to get some surface rust on it so I decided it was time to paint it.
I used Rustoleum charcoal black with the hammered effect. It turned out pretty good. I didn’t bother priming it because I was too lazy. I just used a sheet of cardboard as a back board so the overspray wouldn’t go everywhere. I would definitely spray it while everything is out of the car. I had to remove my seats and harnesses which took some extra time.
Good luck!