You have a couple different options, one being a brushable seam sealer, comes in a quart size can, makes a bloody mess. or you can get a caulking tube of seam sealer, either joint and seam sealer or urethane type sealer. Lordco, Mopac, KMS tools, or any parts store will carry these. I personally like the urethane type used with a caulking gun. if you want to smooth it all out, use a 1\" bristle brush cut short.