I would sand the panels first, probably 220 grit or so, and work up as needed. Wipe it down to remove dust. Clean with acetone or the like to degrease it. Spray with 3-4 coats of self-etching primer, as mentioned by W4rr10r. (It’s most def available at big box stores.) Sand the primer with 400 or so grit sand paper to smooth out the finish on the primer. Then you can top coat with paint of your choice. Spray clear enamel over the paint after a few days, if desired, to enhance durability.