Repainting stock aluminum roof rack

My roof rack looks a little worse for wear, the black paint is peeling off the rails and cross members. I want to repaint the cross bars and rails that came stock on these.

What screws fasten the rails on the roof? They don't look like standard flatheads.

What is the best method for removing the old paint off the aluminum?

Is it a good idea to use spray paint primer and then black rustoleum spray paint on the roof rack?

 

SEM is the paint I often go to. Good clean coverage and lasts well.

Rostoleum is good too.

 

Would powder coating the aluminum work