I would rather be beaten with a rubber hose than have to paint a roll cage inside a car. As Pat alluded, it pretty much is impossible to get all of the "nooks and crannys". I would use some slow reducer to keep down the orange peal.

The best way to do this job is Powdercoat it, if the car is apart. Powdercoat is a lot more durable and about the same in cost if you need to do any media blasting for the paint prep. The paint is going to get chipped and torn up from the belt buckels and the driver getting in and out.