I can say that auto body paint will not work, reason for this is there are too many temperature changes with the fiberglass hard top and the paint will soon lift and peel.
The plastic dip is the same thing mainly because with the temperature changes creating moisture that will be under the plastic dip and soon there will be bubbles and the plastic dip will start looking bad and then peel.
The best thing that I have personally used so far was Dupli-Color spray on truck bed liner. Gives it a texture and is kind of "rubberized". Has been on there almost 2 full years now with no problems.
Sure you can use a primer sealer or a gel coat sealer on the fiberglass if you really want to use automotive style paint on it. But you will still be dealing with the temperature swings because of the fiberglass. Main reason they have so much trouble with the paint jobs on a Corvette.
'87 YJ, 4.2L built and bored, 8" of lift, 8.8 rear, AX15/NP 231J, Tom Woods drive shafts, Flat fenders, 12,000LB winch, Custom bumpers, Rattle can paint job. Never completed...