I use Evercoat Fiberglass resin and pieces of chopped up mat. Apply a bit of resin, then some of the little pieces of mat, a bit more resin, a bit more mat and keep going til your repaired area is a bit higher then the panel you're fixing. An acid brush works good to apply the resin, just make sure you work the mat in so that the repaired area is solid and does not develop an air pocket....