Hi Manning, I used a roller with a very long nap, the kind for applying paint to rough concrete surfaces (even though the obs surface is smooth).  Otherwise it just didn't pick up enough paint.  I did 2 coats, but one problem.  The paint is very heavy, and now with two coats on it, the shutter is so heavy that if it goes past the vertical point the motor can no longer lift it back over the "hump".  So apply the paint sparingly to the shutter.  The paint is amazingly efficient at reflecting heat.

Ted