I am building a SUP, Planking on bottom skin & top skin. The rails are cove & bead. Now that I am shaping the rails I am having some cracks open up. Is there a way to fill these that will look better than seeing dark glue lines under the epoxy. It has been 20 years since I built my kayak. I remember the dark ugly glue lines. I would like to fix it now before glassing.