Consider also that it may only be the gelcoat that has the cracks in it. If this is the case, a sanding to remove the gelcoat is necessary (then rebuild the gelcoat thickness back up). If the cracks go deeper, then I'd suggest sanding (disk sander works good here) it as deep as possible without going all the way through, and then build it back up with cloth or mat sufficiently so to finish it with block sanding, primer, and paint. It's not hard work, just a bit messy.