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Can't you wait till @Airhead tells you the best way to do it.
PS No idea, there is specialist boat paints, but they are of an epoxy type so protect from the weather ingress and wear. Maybe a truck bedliner paint?
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You want to spray it? I don't have any simple advice for that process except, find someone who will spray it for you, in a proper spray shop. It's very nice when done properly. If you don't really need it sprayed then Zinnser stain seal followed by undercoat and top coats depending on what you want to protect it from. Indoors/Outdoors etc. You didn't give enough information to get a decent answer.
WRT my painting ply question- should I just buy the Zinser stuff?