Yes, you always must prime bare fiberglass parts
I used Rustoleme sandable Auto body Primer


If I were doing this, I would First try painting without a complete strip.

sand the cowl to the point all the paint lines were blended, try 220 paper, then hit very light coats of the Primer, it's Lacquer based so it can pull enamals and Polyu paints, but if you build it up with light coats your golden to add the white rattle can paint. Worth a try before you do all the work of completely sanding off the paint,,

good luck