I agree with David that it may be that not booking the paper long enough or that the edges are not booking. I would also try a seam roller but, I would also try seam glue with the seam roller. Seam glue comes in a squeeze tube. If you choose to try the glue I would also suggest that you first re-wet the seams with a spray bottle of warm water. Make sure that you carefully but throughly wipe the seam as when the glue dry it may show shiny. Good Luck!